If you loved Rebirth of Mothra II, try Kamen Rider × Kamen Rider OOO & W Featuring Skull: Movie Wars Core
A bridge between a film you've already seen and one most people haven't. Kamen Rider × Kamen Rider OOO & W Featuring Skull: Movie Wars Core has roughly 3.5× fewer votes than Rebirth of Mothra II — it's a deeper cut, not a mainstream recommendation. Here's what they share, and what the second one does that the first one doesn't.

Rebirth of Mothra II

Kamen Rider × Kamen Rider OOO & W Featuring Skull: Movie Wars Core
What they share
Theyboth carry the playful mood tag, and they sit in Action / Adventure / Science Fiction territory. If that's the register that drew you to Rebirth of Mothra II, the second film will land in a comparable space — through a different lens.
What Kamen Rider × Kamen Rider OOO & W Featuring Skull: Movie Wars Core is
Kamen Rider teams up with others to fight a mysterious enemy. The Pteranodon Yummy attacks, and Kamen Rider W gets help from Ryu. It's a chaotic teamup that somehow works despite itself.