I don’t think there is any plugin that would help.
My current idea is to use the physics behavior for the bubbles. Then just apply a force from every bubble to every other bubble to have them go together. They will just be rigid circles though, not soft.
To make them soft the idea is to draw a larger circle around the bubbles and everywhere those larger bubbles overlap it would become flat. Easier said than done, I have a few ideas but they are involved and I’d have to actually try it out to see if it looks good.
The circle outline could be done as a bunch of sprites as line segments. Filling these outlines could be done by triangulating the polygon shape and then placing two right triangle sprites to fill each triangle.
As is construct 2 doesn’t have the drawing features we want. Namely drawing lines and polygons.
There’s a few plugins that can help do that:
Canvas- has drawline and polygon drawing
Polygon- has polygon
Paster- has draw quad
Custom draw- has draw quad
C3 has only the built in canvas plugin. I’m pretty sure you can draw at least filled polygons with it.