Scab-Clan Giant

In a multiplayer game, you don't choose a single opponent at random. Any creature controlled by any of your opponents may be chosen at random.

To choose a target at random, all legal targets must have an equal chance of being chosen. There are many ways to do this, including assigning each possible legal target a number and rolling a die.

If Scab-Clan Giant leaves the battlefield before its ability resolves, no fight will happen and neither creature will deal damage. Also, if the target creature is an illegal target when the ability tries to resolve, it won't resolve and no fight will happen.