Death Match

Landfall — Whenever a land you control enters, you may have target creature get -1/-1 until end of turn.

Whenever a creature enters, its controller sacrifices a creature or land of their choice.

Whenever another creature you control enters, target creature an opponent controls gets -1/-1 until end of turn.

(As a Siege enters, choose an opponent to protect it. You and others can attack it. When it's defeated, exile it, then cast it transformed.)

Flash

When this Siege enters, target creature an opponent controls gets -13/-13 until end of turn.

Whenever you cast an enchantment spell, you may have target creature get -2/-2 until end of turn.

When this creature enters, target creature an opponent controls gets -2/-2 until end of turn if that opponent controls no other creatures.