A mágica true polymorph diz:
You can turn an object into any kind of creature, as long as the creature’s size is no larger than the object’s size and the creature’s challenge rating is 9 or lower. The creature is friendly to you and your companions. It acts on each of your turns. You decide what action it takes and how it moves. The DM has its statistics and resolves its actions and movement.
Parece-me que diz CR 9 ou menos, e assim criar um Campeão humano CR 9 (Guia de Volo para Monstros, p. 212) é perfeitamente legítimo.
Deixe a bagunça dos gigantes começar.