Skystreamer

Assist exists almost entirely to test a premise: what happens when one player can foot part of another's bill? The keyword lets a second player cover up to of the cost, so the controller can land this for a single white mana while someone else absorbs the rest. Only the paying is shared; the casting, and every decision that follows, stays with the controller. The enter-the-battlefield trigger sharpens the split by handing four life to a target player, which means the controller can bank the life or route it to whoever helped pay, turning the whole cast into a small act of political bookkeeping. Crucially, the keyword reads "another player," not "a teammate," so it works just as well in a free-for-all: the four life becomes the currency in a deal, and an opponent who pays the mana takes the life in exchange while the controller keeps the flier. The 3/2 body is deliberately modest, sized so nobody helps pay because the griffin scares them; the negotiation, not the board impact, stays the interesting part. As multiplayer-only engineering, it sits at the gentle end of a mechanic built to make cooperation transactional rather than incidental. The question it poses is not "is this good" but "who pays, and who benefits," and the gap between those two answers is the entire mechanic working as designed.