Friendly Rivalry

Target creature you control and up to one other target legendary creature you control each deal damage equal to their power to target creature you don't control.

Gimli, Counter of Kills

Trample
Whenever a creature an opponent controls dies, Gimli, Counter of Kills deals 1 damage to that creature's controller.

Gimli, Mournful Avenger

Gimli, Mournful Avenger has indestructible as long as two or more creatures died under your control this turn.
Whenever another creature you control dies, put a +1/+1 counter on Gimli. When this ability resolves for the third time this turn, Gimli fights up to one target creature you don't control.