Flooded Woodlands
The cost scales linearly with the swing, and that arithmetic is the entire mechanic. A green deck pays a land for each green creature it has attacking, charged per attacker: one green creature costs one land, and three attackers cost three lands in total. The bill comes due at the declare-attackers step, before blocks and before damage, so a green player either commits to a swing they can pay for in board resources or leaves their creatures parked at home. Against a wide creature board this converts a lethal alpha strike into an ugly choice: attack with a single threat or strip-mine your own manabase to the bone. The flip side is total irrelevance against anything that isn't green: a enchantment doing precisely nothing. This kind of color-locking enchantment was scattered through the early sets, built to assume a defined opponent and tax that opponent into paralysis. The Dimir identity reads as a deliberate joke at green's expense: the two colors with the least interest in fair creature combat conspiring to make green pay through the nose for the privilege of swinging.
