Skrelv, Defector Mite

The activated ability is where this design actually lives, and it reads more like a bodyguard than a poison enabler. For a single white pip (or two life, if you're tapped out), it grants a chosen color of hexproof, evasion, and toxic to another of your creatures at instant speed. The Phyrexian mana on the activation is the point: the shield goes up at the exact instant an opponent tries to interact, regardless of whether your lands are open. Name red, and the threat you care about shrugs off the burn spell aimed at it and slips past red blockers for a turn; name blue, and it dodges bounce and the wall standing in front of it. That timing turns a fragile combo piece or a lone attacker into something a single removal spell cannot cleanly answer. Legendary creatures built to defend the rest of the board at this cost are unusual, and the toxic grant folds cleanly into a strategy where every attacker chips in poison counters. The 1/1 body, the inability to block, and the one-creature-per-activation limit are the constraints that keep it from being a universal ward: it protects one thing at a time, it cannot save itself in combat, and every turn of coverage costs either mana or life. It defends everything except the one creature holding the shield.