Tweening is probably one of the most useful things in animation. Put 2 frames, tween them, and the in-betweens are filled in. Great!
The problem is, in the testing alpha mode, GIFS can’t be implemented, so I can’t have my Mario character running around very easily in my Mario animation. But just allowing GIFS in the workspace won’t work either, because there appears to be no tweening feature anyway.
I don’t really want to use the beta version because I’m worried that when the editor is finished, the beta won’t be there, and things may potentially be broken. Also, in the beta, you had 4 lines that showed no ease-in or out, ease-in, ease-out, or ease-in-out. Instead of using those, maybe implement an animation curve menu to make it custom so we can have things like ease-out-in, and there are also bounce and elastic.
I also have another suggestion that you can make tweening cooler by somehow letting us tween jumping up. For example, if Mario wants to jump, instead of filling each piece, we can set 2 frames, tween them, and add some correlation to it to make an arc. This can be done by adding a slider for the maximum or minimum height a sprite moves up and down, and a slider for how intense the curve is, from a triangle al the way to a rectangle. Hopefully, somebody understands this.