Mother of Runes

Hand a 1/1 the ability to grant protection from any single color, every turn, at instant speed, and you have built one of white's most durable answers to interaction. The design hinges on two restrictions working together: the tap cost means she can do exactly one thing per turn, and summoning sickness means she cannot do it the turn she lands. That delay is the whole bargain. A creature this flexible coming online immediately would warp every game it touched; forcing it to survive a full rotation first is what lets the rate exist at all. Once active, she rewrites the rules of engagement around her: protection from the chosen color fogs a removal spell, voids a combat block, peels an aura off a creature, and walks an attacker past a chump, all from one untapped permanent. The opponent's only real windows are to kill her while she is summoning sick, or while she is already tapped from a previous activation; respond to her with a removal spell and she simply taps to protect herself, and the answer fizzles. That asymmetry (a one-toughness body that demands an answer at precisely the right moment or not at all) made her a fixture of white creature decks for decades. The template later refined itself: Giver of Runes moved the protection off its own body, trading self-defense for a guardian that shields the rest of the team. The mother came first, and the question she poses (do you have an answer, and is this the moment) has not changed.