User blog comment:B214/Talk About What You Want! 2/@comment-16281343-20141005195634/@comment-16281343-20141017021430

While I myself doesn't believe that it's an independent avatar type, saying that Regulus Nemea took the form of a lion because of willpower is wrong.

Yes, it might have took willpower to move on its own but the ability to turn into a lion from a battle axe is well within the range of abilities of the Sacred Gear.

So far, there's three abilities for Regulus Nemea.

"If you master it, you can split the Earth in a single swing[1], and it can also transform into a huge lion[2].The “Regulus Nemea”! I remember it also had an ability to protect the possessor from projectile weapons[3]."