Time the slam better with the movement and give it less frames so it's faster. Possibly even vibrate or add some crack-effects to it for more force
It didn't occur to me until you mentioned it, but the arm should be treated as an independent entity of the girl. It's a summon pretty much, and does things at it's own pace.
You have a very pose-to-pose animation style, but you for whatever reason smooth out and add frames during the fastest movements, yet the motions which should be slow are too quick.
I feel as though you are lacking anticipation of motion too. Too little wind-up before movement, especially if you're using a super-exaggerated animation style.
Here's how I'd start to approach in fixing the issues. Added a small lean back before the big movement at the beginning, removed a few frames, duplicated a few frames, added a small anticpatory motion before the raised arms. I removed the end for the sake of saving time. Obviously it's not polished up, but I hope I could get my points across.
Hopefully, I could help. By the way, are these made for anything specific, or just for fun?
I played around with the removing of the frames, and changed some things that I felt needed a change. The skeleton arm is now supposed to be a sort of bladed arm and has a more detached movement, the girl disappears in a different way other than just breaking apart, and I completely reworked the last bit to have a bit more action.
As for what they are, they're pretty much power displays for the characters I've designed for the sake of world building, animation/general art practice, and just cause it's fun. For example, this character is associated with demons and spirits (They're all based on general RPG archetypes, in order Hero
), which is why she had horns, and why her hair goes white. In this, she uses her magic to make the portal, summoning one of her demons (the arm), uses spirit magic/another demon to become ghostlike, then summons the black and white demon.
When I make another set of these, I plan on utilizing their other powers/traits/etc. with what I've learned here. There's a lot of stuff I couldn't execute properly or as well as I wanted to, so I'll try again.