The MMPR Megazord combined with the Dragonzord takes on the combined form of the Astro and Delta Megazords.
The MMPR Megazord combined with the Dragonzord takes on the combined form of the Astro and Delta Megazords.
I haven't watch PRIS for years so I'm not sure but I'm going to say Mega Dragonzord. As I recall that particular Zord configuration was basically undefeated. Plus it took down some very powerful monsters, including Mutitus in his powered-up form.
https://www.youtube.com/watch?v=t1HlVgzCcOs