The dummy object is the easy way. And it might be the best way.
Althaught i almost never use it, it is more events, it is an object more to care for.
I just make all the frames in every animation the same in size. Normaly, i do that when i make the graphics.
But you can do this in Construct. Just find the biggest frame. Scale it to its size, (button in the ribbon), image = allign to center, check to do it for the whole animation. Do this (with this size) in every animation. If this gives problems as in the position of the animated thing gooing to slide, then a helper object will not help too.
For the origin, set it once in some frame, right click it in the image points list, apply to all animations. It is best, when working with a platform, to set the origin at the bottom. But within the collision polygones.
For the collission polygones. If they differ to much, the animation will animate the character into the solids. Result: the darn thing is stuck. With a helper object you have 1 collission polygone anywayz. So, you can as well set 1 collission polygone on all frames in each animation. Go to a frame that concerns you most, make the polygone. Richtclick the polygone (in image editor) set to all animations.
If you need animated collission polygones, thats is possible. (not with a helper object). You just need a lot of frames in the animation. And animations that are up speed. You have to animate the polygones in a way that they are no more differend frame by frame by kinda 2 pixels. That should work.
There is a polygine plugin:
But i dont know if it is up to date, and i never used it myself.