Brave-Kin Duo

A one-drop pump machine, and the sorcery-speed clause on the ability is the whole balancing act. Repeatable +1/+1 effects that could fire at instant speed have always been dangerous in aggressive decks: they double as combat tricks, punishing every attack and block the way an untapped mana dork with a stinger would. Restrict the same effect to your own main phase and it stops ambushing anyone. It can only build a board on your turn, so the opponent gets to see the threat before deciding how to answer it, which turns a would-be blowout engine into a slow, honest grind. What is left is a creature that quietly widens the gap in a go-wide start: tap it before combat, hand a lord-sized buff to whichever attacker needs to punch through, and repeat every turn as long as it survives. The 1/1 body is small enough that it dies to nearly anything, which is the price at the far end of the deal; the engine only runs while a single point of toughness stays on the board. It belongs with the white one-mana creatures whose real work happens through an activated ability rather than combat, closer to a slow anthem you have to protect than to a beater you cast and forget.