Ok, so i just got enough mystic rings to max out a new red hero. I have decided it should be either Tyr or Baldur.
The other red heroes i got maxed:
Garnet, Santa Claus, Jean-Francois, Mitsuko, Red Hood, Gefjon.
None of them will be a part of my defense team, as i got Onyx, Cobalt, Heimdall, Garnet and Joon there. My next red will mainly be used as a offensive attacker in wars/raids