Polymorph by Samuel Leng Polymorph is generally not seen in Premodern due to Oath of Druids, Show and Tell, Natural Order, and Reanimate providing more efficient ways to cheat out creatures, but I like Samuel Lengs attempt
Goldin Auctions is a well-known auction house that has brokered many valuable Pokemon items
It can be used both offensively and defensively (though a defensive Rift with no follow-up remains a bugbear for players everywhere)
Looking at my cube, there is critical mass for: Goblins (R) Humans (all) Warriors (WBR) And, with some effort, other tribes could get critical mass running only cards that are cubeable by themselves, keeping the Poison effect to a minimum: Soldiers (W) Wizards (U) Shamans (RG) Vampires (B) I'm fine with dedicating 2-3 slots per color so each of these tribes have a Lord or some other linear effect as a nod to play them (Goblin Chieftain, Champion of the Parish, Chief of the Edge) but I don't want this cube to be mainly tribal, just have an extra layer of synergy that cares about the creature type line at a low opportunity cost
Being an instant also lets you leverage the ability by holding up countermagic, card draw, or bouncing your opponents board states to remove all blockers before your turn