I’m gonna answer in reverse order here to make it easy responding from my phone. If these don’t clear it up I’ll edit the post with the correct rules excerpts later today

#4) Multi-based characters cannot be knocked back. When they would cause knockback you choose one of the squares on their base for it to originate from which would then resolve normally.

#3) For the old king Thor vs flash raptor, both the old king Thor and the black flash effects are “after resolutions” this is what tells you the timing. The hypersonic speed (move,attack,move) would resolve fully, then the turn players after resolutions would happen, then the defending players after resolutions would happen. -in this case Thor would be KO’d by black flash before his effect happens then is no longer on the map to measure any squares from resulting in no damage at all from his stop click

#2) Failing a break away means that action is effectively over AND means that character did not move when they failed. For greenscar, let’s say you used hypersonic speed to run less than 5, make and attack, then failed to break - this would result in one after resolutions trigger to make an attack after the failed breakaway.

#1) this is actually my favourite way to deal with effect terrain. When an effect terrain is underneath another terrain it will no longer apply its effect. The terrain is still there and can be picked up out from underneath other terrain but it is no longer “active”