Decided to slow down all the frames with the blink by 0,4 seconds (since they were 0,4 seconds long in the first place and I wanted to double the time they last) so I wouldn't have to add new frames, and I think it looks much better this way. Also decided to do some other modifications. 

Flash looks really cool, but the blink is not so amazing. Typically, you barely see a blink go down, although it's ok to have a few frames on the way back up. Try cutting the down motion to a couple frames or so and it should look much snappier. Pretty cool entry otherwise, seems like a real step up from your previous work. 

Would have liked a bit more of a 'reveal' when the lightening strikes, but I like it. :)

Not really into animation so my advice could be unuseful... I think just repeating the lighting 2-3 times in a second could help :)

I did already try experimenting with speed of individual frames (so I'd try to not make them too fast or too choppy), but I'm guessing this somehow slipped my mind (probably thought it was fine as is).

I was going for a quick small dramatic flash (inspired by the one seen here), but since my piece has 2 different frames with the (partially) uncovered character (one is used for a fade-out) and the flash seen in the reference cutscene has 1, I don't know how will I slow it down and pull it off effectively at the same time without having to make another frame or something.

If you can, please provide tips on this since I'm practically clueless on what to do. Thank you in advance :)

The animation is really quick... too quick maybe to appreciate the hidden parts of the body.