Brittle Bone

Creatures your opponents control get -X/-X until
end of turn where X is the number of Warpstone tokens you control, this cannot lower an enemy creature's toughness to less than 1. If mana from
only Warpstone tokens was used to cast this spell it
can lower enemy creature's toughness to less than 1.

An ancient Skaven spell that enables the Wizard to weaken their target's bones, causing different effects depending on who they are. All will suffer horribly, however.