Mistform Stalker

The shapeshifter as tribal swiss-army: where most Mistform creatures lock you into a single payoff (Mistform Ultimus is every type at once, Mistform Wall just blocks fliers), this one buys its versatility by the activation rather than the printing. One generic mana names any creature type, so it dodges or feeds tribal pumps, slips under "destroy target Goblin," or becomes whatever your lords want it to be, then resets each turn for the next problem. The second ability is the closer: a four-mana investment that turns the 1/1 into a 3/3 flier on the spot at instant speed, which lets a board-stalling chump suddenly carry the air. The tension is that both abilities want the same untapped lands, and the body is fragile enough that the type-changing is more often a defensive feint than an offensive engine. As a piece of Onslaught's tribal-matters block, it reads as the designers' attempt to give Illusions a way to participate in every other tribe's mechanics without committing to one, an ancestor of the broader Changeling idea that would later collapse "becomes every type" into a static keyword. Here the effect is still manual, still telegraphed, and still costs you a mana each turn to maintain the fiction.