2-Mana Removal When it comes to cheap, reliable answers, Infernal Grasp and Go for the Throat are two of blacks best options
It doesn't prevent abilities from being activated or from triggering later in the turn, and it has no effect on static abilities
Chromatic Lantern and Arcane Signet are going to be good rocks here, but I wouldn't play any signets or anything like that and I don't think we need bad three-mana rocks like Manalith or Basically Manalith (Darksteel Ingot)
More specifically, "the Disney characters that you band together as an illumineer will be called 'Glimmers'"
More Expensive You could go with popular cards like Arwen, Weaver of Hope and Aftermath Analyst but those don't feel maximized with Lathril
Secondly, the Black Lotus is one of the most powerful cards in the original MTG game, so powerful in fact that by playing it with the right combination of cards, a player could win the game on their first turn