Weve seen plenty of creatures like this over the years: Doomed Traveler, Blisterpod, and even Infestation Sage in Foundations
List of All Types: Avatar, Wizard, Elemental, Plant, Ooze, Beast, Dryad, Elf, Shaman, Elephant, Human, Druid, Giant, Spirit, Wall, Incarnation, Treefolk, Warrior, Ape, Goat, Hydra, Cat, Warrior, Boar, Eldrazi, Demigod, Elk, Wurm, Dragon, Spider, Dinosaur, Dog, Phyrexian, Fungus, Snake, Thopter, Rhino
They mutate into the creature on top plus all abilities from under it.) Reach, trample Whenever this creature mutates, destroy target artifact or enchantment an opponent controls
Card choices prioritize how pieces interact with your commander and with each other (e.g., self-mill as draw, modal spells for double Kess value) instead of blindly jamming the usual staples
Probably best used in other formats