He hasn't revealed it for a reason
I'm thinking Loki's other Hybrid is probably a quadruped, since many Western Dragons walk on all 4 legs.
So far, we have a flying form, and a bi-pedal form.
I think the 1st Hyrbid will have him on all fours. Fits what we saw in the flashback:
Clearly running on all fours here when going to the Throne Room
While holding Harald, it looks like a quadruped standing on its rear legs.
Finally, it's been awhile since we've gotten 4-legged Zoan Action
@Mr. Reloaded ayo we might have another Quadruped Zoan to simp for, along with Yamato, let's get it