Spacehorn

"???" Elements: Shadow, Mech, Crystal, Spectral

This monster can be bred with two Double Elements.

Arackulele + Flutehog

Shadowmorph + Bellowfish

Boodoo + Drummech

However, it can be bred with a Single Element and a Triple Element.

Rillaquina + Grumpyre

Stong + Reebro

Sitarthon + Jeeode

Gockonspiel + Spectgon