Some parts are snap in, others are peg in and others are 'clamp' in. The result is overall pretty solid, much more so than the original Energon Bruticus set up.
There is only one part replacement as LiegePrime mentioned, the Energon Bruticus head needs to be unhinged and remove from Onslaught; then replaced by the new head but since it's a 'snap out' part, you can easily put the old head back in but who would want to do that?
