Mechtitan Core You can play Mechtitan Core with Thopter tokens or other things that you dont mind exiling, but the strength of the card is in bringing the other artifact creatures and/or Vehicles back onto the battlefield so you can have the tasty triggers
Crew 1 Cosima's ability triggers only if Cosima is on the battlefield at the beginning of your upkeep, and you may exile Cosima only if it is still on the battlefield as the ability resolves
Either that, or just use it to punish other players while their current board is empty
I have no serious complaints about this deck
Searches and fetches become useless with mills from Ashiok, Dream Render. Meanwhile, while Narset, Parter of Veils and Spirit of the Labyrinth locks card-draw limit for all parties
If you can activate its encore ability while multiple players are still in the game you'll be able to clear the board of any big threats, while gaining a significant chunk of life