Good arkadions?

So I just beat arborun and I’m looking for good arkadions in that location or before that. Preferrably good all through the game because all my arkadions are lv 40+ and at least 8 stars.

Rexy, which is one step to the left of the Cave of Ages, evolves into a good 8.5 star monsters. Once you hit the wastelands, you can get Nilo in the mountains, and then musharoo near the bridge, and combine them for a very good monster

What do they fuse into?

Nilomoth but you need the recipe for it