Mantellum

Whilst Mantellum is untapped, untapped
creatures you control have Hexproof.
Whilst Mantellum is tapped, tapped creatures
you control have Hexproof.
We found a possible in, a weak Case Fifty-Three that
Thinkers couldn't see. We helped him get stronger,
mostly by giving him a chance to figure out how it
worked, and then we moved fast.