I recently got back into Cthulhu and was very interested in the key and the gate set. I noticed right away Yithian mill was ......very fast. With modifications you could also have pretty awesome Tesla deck "again with key and the gate basis".

My question is this:

What would you use to modifiy the typical yithian mill deck to suit Tesla? Obviously you would trade out intersteller migration for tesla. You would need a way to kill him off. (maybe deep one assault of a gift of knowledge). Can someone assist?

Plague Stone is a good option. It's a great card that can buy you time against many decks while also serving as a Tesla killer. I'd probably splash Cthulhu since it has Deep One Assault and Flooded Vault to find Plague Stone (among other supports). Deep One Rising is a bit slow but transient resources can help with it. If you want to keep it mono-Yog, Lev'l 15:13 will help. For Agency, A Small Price to Pay is cheap and effective.

Summon Spectral Hunter. I think Tesla is too easy to counter to be the main focus of a deck, maybe in addition to Migration. Frozen Time, Pushed Into the Beyond, anything that makes you sacrifice or discard, works on him, and no success tokens.