I know it's possible to execute a super move once the lightning bolt is flashing. Trouble is, I haven't been able to sort out how. Anyone have any insight?

Nevermind - I found the answer here: https://segaretro.org/Mighty_Morphin_Power_Rangers:_The_Movie_(Game_Gear) There's a handy pdf of the manual.

WHAT THE F !!! :D 5 days ago you were unable to do super moves and now you just destroyed me by more than a minute !!

I practiced a fair bit. I really like the other GG power rangers game, so I play/run it a lot to wind down in the evening. A lot of my skills on that one applied to this one as well. The Hard mode on this one is a lot more brutal with the limited continues. I mean wow, that was a rough fight against the final boss.