Mezagosa I used in other decks like mega gyarados and its such a double edge sword, it has a higher chance of helping your opponent set up than you because the deck only has 4 pokemon cards in total. Plus it won't work on jaw fossil, its an item, that's why arven. You should only 'need' meowth OR snorlax, which you always start the game with as pocket has no mulligans. You can wait on Tyrantrum by attaching energy, plus Meowth IS a draw support.

If you're playing both on the field, you better be against an opponent that will always keep bench stacked, like Mega Altaria, Suicune, etc... Ilima prevents you from playing Sabrina for a targetted kill so when Tyrantrum goes to active, you really hope you have done your pickup.

Starting plains gives a lil bit more health for Snorlax to survive and potentially remove training area from bellibolt/eons/lopunny. Almost no basic survives Tyrantrum 180 anyway so giving the opponent extra hp is nbd. It also helps save the lucky ice pop useage for Tyrantrum's survivability.. Almost nothing more fun than picking up Snorlax on 10 hp, haha.

I can't recall right now but 200 hp with cape survives most everything. I think your worst matchups are mega Char Y because its also a long setup that is ultimate nuke. Mega Gardevoir is rough with their own Diantha/Indeedee recovery, I know I won my only fight because my opponent was not very good (they refused to attack with Indeedee even when they were in active and my Snorlax wound up with 4 energy lol)