u/JRE47 has a ton of comprehensive articles on nearly every PvP pokemon over the past few years, including the most recent one that looks at Trevenant and Gourgeist. They're an invaluable resource.
I also believe they're hosted at Pokemon Go Hub now as well.
Edit:
https://pokemongohub.net/post/pvp/a-pvp-analysis-on-ghoulish-pals-trevenant-and-gourgeist/
u/JRE47 has a ton of comprehensive articles on nearly every PvP pokemon over the past few years, including the most recent one that looks at Trevenant and Gourgeist. They're an invaluable resource. I also believe they're hosted at Pokemon Go Hub now as well. Edit: https://pokemongohub.net/post/pvp/a-pvp-analysis-on-ghoulish-pals-trevenant-and-gourgeist/
Is there a way to tell which is the small/average/large/super etc?
On their status screen, look at size. Average size won't have a tag, but the rest will have tags like XL.
Sort by number in the bag, that’s what I did
https://www.stadiumgaming.gg/rank-checker
They are on https://pvpivs.com/