I started my journey into the format a couple years ago playing Golgari Gardens, and I always kept an eye open on the evolution of the archetype
Owner's Pokmon have no unique mechanics on their own, but they often have synergies with trainer cards featuring their owner and other Pokmon with the same owner
Leyline of the Guildpact might not be the most powerful, but it gets the MVP award on this list because it fixes your mana in one card
Whenever you cast a black spell, put a +1/+1 counter on K'rrik
Commune with Lava scales well with the game, and can either fill a gap in your curve or set you up for one huge turn
Sword of Truth and Justice is another one that is pretty good with Venser as the commander since it gives him (conditional) evasion, proliferates, and adds +1/+1 counters to grow your creatures which the deck has very few ways of doing, but I absolutely would not spend $30+ for the card, it's not that good