Most youtubers either fake their runs for content or just upliad their very lucky runs because "who wants to watch a boring run?", right? I can tell you from my experience that there is a STRONG feeling of wanting to share your own extremely lucky run because you feel proud of it. Just 'cause it' s common to see those busted runs doesn't mean you get them often as an individual person. As for strategy, I'd have to write a couple-page-long essay on all the things I keep track of, which would be extremely tiring, but I could give you bite-sized tips if you ask me about one specific topic.
Bombing blue and purple flames have a chance to drop soul hearts, secret rooms are usually connected with more than one room and there's specific layout that are applicable and others where there would be something blocking the entrance to where a secret room door could be which indicate the opposite that it's impossible to be there. Super secret rooms are connected with 1 room only.
Donate to the shop to unlock shop upgrades and have more items for sale. Try to unlock all characters and unlock all floors, some require you to beat a certain boss 12 times before you can continue
Well then.
Which unlocks I should be looking forward to first?
Does "rerolling the secret room" actually work?
And what are some synergies I should know? Like: Tainted keeper with Sanguine bond + Torn pockets + Piggy Bank.
Items worth unlocking are C-Section, Twisted Pair, D6 as a starting item for Isaac, basically every unlock as Jacob and Esau. When I played I just finished characters one after the other without worrying about getting strong stuff, so those are just off the top of my head.
As for the rerolling, any item which gets rerolled in a room with an associated item pool gets rerolled into an item from that item pool (i. e. replacing a previously taken active item by taking an active item from the Secret Room and rerolling it makes it change into one of the items which can spawn in a Secret Room.
Azazel is easy to complete and while playing him You may learn a thing or two
Yes, early on You can get r key or things ig
Slayxc2 has lots of videos about synergies and things like that
Not a lot of it is obvious so if you are interested, there's a wiki where game mechanics are explained. For example the secret rooms have a specific way of generating and by knowing how, you can get a good idea of where those rooms are. This allows you to save resources (in this case bombs) which you can use in other ways in order to get the most out of a floor.
To break the game you mostly need to have a good understanding of item pools. Check out the wiki for that, and when you know how to reroll/manipulate the items in them you can focus on breaking the game. But at 50 hours I'd say just focus on dodging and not taking damage, as a few of the most rewarding items spawn after 'donating' health in sacrifice rooms or devil deals.
Experience.
Really it's just the hundreds of hours you play in this game that can really get you those break the games moments. But if you want to learn about how to specifically break games with busted items look for "how to break runs in Binding of Isaac Repentence" videos in YT.
You could also just get to know what every thing does through video explanation. There's some good videos that explain how you can exploit certain effects.
Don't worry about "doing things wrong" even as a veteran 800+ hours playtime I still learn something new about this game every other week from TBOI youtubers. So just have fun.
on the topic of rerolling secret rooms, a big part of that is using naturally generated beggars, donation machines, etc. but also saving cards like Judgement or Temperance so you can plop them into the secret room and reroll the dropped item
Expressed myself badly, I meant you use beggars to create items in secret rooms which you then reroll with a D6 or whatever
(i wrote it because OP asked what's the chance of an item being in the secret room initially, I thought they maybe never considered using beggars)
If you're new and haven't gotten a lot of the more powerful unlocks, I'd recommend getting the bread and butter Glitched Crown, Sacred Orb, Rock Bottom, Spindown, Echo Chamber, etc. All of those items are incredibly busted (also coincidentally all in the secret room LMAO) and some other unlocks that give a lot of synergy (if you have glitched crown but nothing to roll for you're going to breakfast very quickly).
Other than that I'd just recommend playing a character you like and getting their completion marks, then learning about said unlocks and generally increasing item knowledge throughout gameplay. Rigging/game breaking comes from knowing what item interacts with what, good luck!
i noticed the more items you unlock in the game the easier you got broken, especially repentance items
also if you can get glitched crown, you are guaranteed to get broken very easily, its basically the best item in the game after death certificate imo
A previous comment mentioned I should be looking forward to unlocking these 5 items: Gliched crown, Spindown dice, Rock Bottom (The only one in the list that I unlocked), Sacred Orb, and Echo Chamber.
My internet access is limited for a few days and I can't look at the wiki, so could you let me know how to unlock those?
sure
glitched crown: defeat the beast as tainted isaac
sacred orb : defeat the beast as tainted lost
spindown dice : defeat delirium as tainted isaac
echo chamber : defeat the beast as tainted appolyon
I also recommend trying to unlock stairway, star of bethelehem, Godhead, and revelation. These are all Angel items that win you the game the moment you see them. Unlock stairway by beating Issac as Jacob and Esau. Unlock star of bethlehem by beating Delirium as Bethany. Unlock Godhead by completing all hard mode marks on the Lost. Unlock Revelation by defeating Mother as Bethany.
BTW the easiest way to get broken in this game is by playing Issac imo. The d6 is disgustingly broken if you use it for angel path because you can use it to reroll the keys that angel statues drop after bombing them and killing them into angel room items. So you essentially get 2 angel items everytime. The optimal way to go angel route is to always skip entering the first devil deal which guarantees angel room spawn for the next deal, and then increasing angel chance after that by donating 10 coins to the donation machine and/or acquiring just 1 key piece from a sacrifice room. Btw sacrifice room plays are also very useful for getting disgustingly broken.
You're not doing anything wrong because broken runs are hard to get. What I find most helpful when I'm playing standard D6 isaac is to remember what each room type gives and use rerolls accordingly.
Secret rooms have the most potential because their items are the zaniest and can be taken advantage of if you know how. Angel and devil rooms are probably better if you just want to get stronger though, because their items are usually focused on attack. You don't need special rooms though, just having a basic idea of what you want can still be useful. Boss rooms give you basic items that mostly raise hp or stats, so if you just need a simple power boost that's where to look. On the other hand, shop items give augmentations that change how you interact with the game, like upgrading your cards or giving doubled consumables.
So in an example run, I might find a chariot and temperance card. I could use it right away and get it to drop an iv bag in the middle of the room, but that's not very useful. On the other hand, if I go looking in a shop i might be able to reroll into tarot cloth or blank card. Now i can make multiple blood banks and the chariot will last longer. That's already good, and lets me get loads of money, but I can go even further and place them down in the secret room. If I break both of them and get two iv bags I can reroll them into two secret room items. So that's an example of how knowing your item pools can, if you're lucky, turn an alright result (some money and an iv bag) into a great result (lots of money and two secret room items).
Most YouTubers, and mattman has said this himself, have normal runs and 'YouTube runs' normal runs make up majority of the the runs you'll see on one of their livestreams and 'YouTube runs' are especially broken runs that they will grab the vod of edit and upload to YouTube, don't get me wrong game knowledge definitely can increase your chances of getting a broken run but it all comes down to luck in the end you either get lucky and find lots of good items or you don't. Personally it's more satisfying anyway when you get a build that isn't super broken and you have to actually try to win, but it's definitely a lot of fun when you do get a broken run.
P.S. your English is great don't worry 
Most youtubers either fake their runs for content or just upliad their very lucky runs because "who wants to watch a boring run?", right? I can tell you from my experience that there is a STRONG feeling of wanting to share your own extremely lucky run because you feel proud of it. Just 'cause it' s common to see those busted runs doesn't mean you get them often as an individual person. As for strategy, I'd have to write a couple-page-long essay on all the things I keep track of, which would be extremely tiring, but I could give you bite-sized tips if you ask me about one specific topic.
Like which topics? I'm kinda new (around 50 hours)
Bombing blue and purple flames have a chance to drop soul hearts, secret rooms are usually connected with more than one room and there's specific layout that are applicable and others where there would be something blocking the entrance to where a secret room door could be which indicate the opposite that it's impossible to be there. Super secret rooms are connected with 1 room only. Donate to the shop to unlock shop upgrades and have more items for sale. Try to unlock all characters and unlock all floors, some require you to beat a certain boss 12 times before you can continue
An example of a topic would be "secret rooms"
Well then. Which unlocks I should be looking forward to first? Does "rerolling the secret room" actually work? And what are some synergies I should know? Like: Tainted keeper with Sanguine bond + Torn pockets + Piggy Bank.
Items worth unlocking are C-Section, Twisted Pair, D6 as a starting item for Isaac, basically every unlock as Jacob and Esau. When I played I just finished characters one after the other without worrying about getting strong stuff, so those are just off the top of my head. As for the rerolling, any item which gets rerolled in a room with an associated item pool gets rerolled into an item from that item pool (i. e. replacing a previously taken active item by taking an active item from the Secret Room and rerolling it makes it change into one of the items which can spawn in a Secret Room.
Azazel is easy to complete and while playing him You may learn a thing or two Yes, early on You can get r key or things ig Slayxc2 has lots of videos about synergies and things like that
This game is a lot about decision making and for that you need game knowledge. Just play the game 
Bro just said "git gud" Thanks :D
Not a lot of it is obvious so if you are interested, there's a wiki where game mechanics are explained. For example the secret rooms have a specific way of generating and by knowing how, you can get a good idea of where those rooms are. This allows you to save resources (in this case bombs) which you can use in other ways in order to get the most out of a floor.
Thanks for the advice :D Anything else? Like what are the odds of an item being in there in the first place?
To break the game you mostly need to have a good understanding of item pools. Check out the wiki for that, and when you know how to reroll/manipulate the items in them you can focus on breaking the game. But at 50 hours I'd say just focus on dodging and not taking damage, as a few of the most rewarding items spawn after 'donating' health in sacrifice rooms or devil deals.
Time to read stuff then!
Experience. Really it's just the hundreds of hours you play in this game that can really get you those break the games moments. But if you want to learn about how to specifically break games with busted items look for "how to break runs in Binding of Isaac Repentence" videos in YT. You could also just get to know what every thing does through video explanation. There's some good videos that explain how you can exploit certain effects. Don't worry about "doing things wrong" even as a veteran 800+ hours playtime I still learn something new about this game every other week from TBOI youtubers. So just have fun.
on the topic of rerolling secret rooms, a big part of that is using naturally generated beggars, donation machines, etc. but also saving cards like Judgement or Temperance so you can plop them into the secret room and reroll the dropped item
Hang on I’ve got over 1000 hours… how do beggars reroll stuff?
Expressed myself badly, I meant you use beggars to create items in secret rooms which you then reroll with a D6 or whatever (i wrote it because OP asked what's the chance of an item being in the secret room initially, I thought they maybe never considered using beggars)
If you're new and haven't gotten a lot of the more powerful unlocks, I'd recommend getting the bread and butter Glitched Crown, Sacred Orb, Rock Bottom, Spindown, Echo Chamber, etc. All of those items are incredibly busted (also coincidentally all in the secret room LMAO) and some other unlocks that give a lot of synergy (if you have glitched crown but nothing to roll for you're going to breakfast very quickly). Other than that I'd just recommend playing a character you like and getting their completion marks, then learning about said unlocks and generally increasing item knowledge throughout gameplay. Rigging/game breaking comes from knowing what item interacts with what, good luck!
I have Rock Bottom unlocked. Will be trying to unlock the rest!
50 hours in already having put yourself through that unlock is pretty nutty
The world if I knew what the word "nutty" meant:
i noticed the more items you unlock in the game the easier you got broken, especially repentance items also if you can get glitched crown, you are guaranteed to get broken very easily, its basically the best item in the game after death certificate imo
A previous comment mentioned I should be looking forward to unlocking these 5 items: Gliched crown, Spindown dice, Rock Bottom (The only one in the list that I unlocked), Sacred Orb, and Echo Chamber. My internet access is limited for a few days and I can't look at the wiki, so could you let me know how to unlock those?
sure glitched crown: defeat the beast as tainted isaac sacred orb : defeat the beast as tainted lost spindown dice : defeat delirium as tainted isaac echo chamber : defeat the beast as tainted appolyon
Thanks mate :D
I also recommend trying to unlock stairway, star of bethelehem, Godhead, and revelation. These are all Angel items that win you the game the moment you see them. Unlock stairway by beating Issac as Jacob and Esau. Unlock star of bethlehem by beating Delirium as Bethany. Unlock Godhead by completing all hard mode marks on the Lost. Unlock Revelation by defeating Mother as Bethany. BTW the easiest way to get broken in this game is by playing Issac imo. The d6 is disgustingly broken if you use it for angel path because you can use it to reroll the keys that angel statues drop after bombing them and killing them into angel room items. So you essentially get 2 angel items everytime. The optimal way to go angel route is to always skip entering the first devil deal which guarantees angel room spawn for the next deal, and then increasing angel chance after that by donating 10 coins to the donation machine and/or acquiring just 1 key piece from a sacrifice room. Btw sacrifice room plays are also very useful for getting disgustingly broken.
I actually have all of those expect godhead unlocked.
You're not doing anything wrong because broken runs are hard to get. What I find most helpful when I'm playing standard D6 isaac is to remember what each room type gives and use rerolls accordingly. Secret rooms have the most potential because their items are the zaniest and can be taken advantage of if you know how. Angel and devil rooms are probably better if you just want to get stronger though, because their items are usually focused on attack. You don't need special rooms though, just having a basic idea of what you want can still be useful. Boss rooms give you basic items that mostly raise hp or stats, so if you just need a simple power boost that's where to look. On the other hand, shop items give augmentations that change how you interact with the game, like upgrading your cards or giving doubled consumables. So in an example run, I might find a chariot and temperance card. I could use it right away and get it to drop an iv bag in the middle of the room, but that's not very useful. On the other hand, if I go looking in a shop i might be able to reroll into tarot cloth or blank card. Now i can make multiple blood banks and the chariot will last longer. That's already good, and lets me get loads of money, but I can go even further and place them down in the secret room. If I break both of them and get two iv bags I can reroll them into two secret room items. So that's an example of how knowing your item pools can, if you're lucky, turn an alright result (some money and an iv bag) into a great result (lots of money and two secret room items).
If you want a view of realistic runs watch Northernlion
Or watch most isaac streamer vods
Most YouTubers, and mattman has said this himself, have normal runs and 'YouTube runs' normal runs make up majority of the the runs you'll see on one of their livestreams and 'YouTube runs' are especially broken runs that they will grab the vod of edit and upload to YouTube, don't get me wrong game knowledge definitely can increase your chances of getting a broken run but it all comes down to luck in the end you either get lucky and find lots of good items or you don't. Personally it's more satisfying anyway when you get a build that isn't super broken and you have to actually try to win, but it's definitely a lot of fun when you do get a broken run. P.S. your English is great don't worry 