With indestructible baked in, Kotis is hard to deal with, and once you start to buff it up with equipment or auras, the payoff is massive: You exile and cast spells from opponents libraries for free
No card is essential either, you really want Ishkanah and you quite want some others but you are totally fine without
Pikachu variations for Base set were decently noted from the start, if you checked a couple of different sources
Master-setted Stellar Crown currently working through 151, Black & White, and Prismatic Evolutions
Later, a 4-mana investment gives you an Archaeomancer-like effect, so you can get whatever you need back
This one-two punch shows off what backgrounds can do, even in a mono-colored deck