Crystalline Mantle

Whenever a commander creature enters play
under your control, you may have Crystalline
Mantle become an Aura and attach it to that
creature.
If Crystalline Mantle is an Aura, it has
'Enchant creature', 'Enchanted creature has
hexproof', and 'If enchanted creature leaves play,
return Crystalline Mantle to the battlefield
under your control, it is no longer an Aura'.