These are some ideas my son and I have been working on for Heroica mounts. They include an eagle, horse, panther, mecha, sphinx, cow, bear, spectral horse, ram, hellion, wolf, gryphon, and kodo. They cost 20g and allow a hero to leave an engagement, and move 1 extra space. They cannot be killed.
I have built the horse with basic parts but the rest require some hard to find pieces (in the right colour). Each is designed from a 1x3 template to fit either on 2 squares or stand free over top the bump on a single space. A microfig fits on the sadle bump on roughly in the middle. They stand 3 bricks high or equal to a microfig.