It will come to the defense of all wild things, from the shivering wren to the towering giant.

Thorn Mammoth

Trample
Whenever this creature or another creature you control enters, this creature fights up to one target creature you don't control.

The List

Throne of Eldraine

If the target creature is an illegal target when Thorn Mammoth's last ability tries to resolve, the ability doesn't resolve. If Thorn Mammoth is no longer on the battlefield, the target creature won't deal or be dealt damage.