If the target creature is an illegal target when Thorn Mammoth's last ability tries to resolve, the ability doesn't resolve
You'll draw, nice, and then you can exile an artifact or critter from your hand and make a token copy that's a 3/3 Golem artifact too
Yawgmoth comes to mind, especially the build running Birthing Ritual and token generators
If a bounty cant be completed by the player that turns, it is amped up with a better reward across four levels
Mystical Tutor One mana to tutor for any instant or sorcery is a great deal
Instead, a creature is given the designation of Ring-bearer. The creature chosen to be the Ring-bearer remains the Ring-bearer until you either choose another one, it leaves the battlefield, or leaves your control