Tainted Well

Spend the three mana, draw a card, and one of your lands becomes a Swamp until the Aura leaves: a slow but card-neutral way for a black-splashing deck to firm up its colored count when its nonbasics ran in the wrong direction. The cantrip on entry is what keeps the trade honest, since you refund the card you spent rather than eating a clean tempo loss. The instructive quirk lives in the "enchant land" wording, which never asks the target to be yours. You can drop it on a basic Swamp you already control and treat it as a pure cantrip with no fixing at all, or aim it at an opponent's utility land, retyping it to Swamp to shut off whatever land-type or color requirement it was feeding. Removal does not punish you as hard as the rate suggests: because the draw is already banked, an answer to the Aura (or to the land beneath it) is at worst a one-for-one. The fragility is real (the retype lasts only as long as the Aura survives, and the setup happens at sorcery speed), and that is precisely why color-fixing migrated to lands that fix themselves rather than Auras that fix something else. This is fixing from a stretch of design when changing a land's type cost a whole card, before dual-land templating absorbed the job and made the spell unnecessary.