OK, see I was playing this like the super battle droids and looking for something to "highlight" to throw him against (like the blue circles you get with them). There wasn't that "clue" about where to throw him, so I probably only did it by accident.
The final fight with Grevious where he forces Obi Wan onto the bridge. Look to see what you can throw at him. This will take a silver heart. Next pick him up with the Force and throw him against a wall or something else. This will take the red heart. Do this until he is defeated.
Follow-up - so, we got through, but we have NO idea how we managed to kill Grevious. I basically started hitting him with everything in sight (as Obi-Wan) and eventually we killed him off in that area -and went on to finish the level.
But, it would be nice to know for future play what the sequence of hits/objects/events needs to be to get through here.
OK, my Dd and I are playing this together and having a blast. But we're stuck at the fight with Grevious and the Clone Trooper - probably toward the end. We've completed the split-screen section - where one side is Anakin and the other Obi-Wan (who fights Grevious).
We know that if Obi hits Grevious with a forced container, it turns the silver/mechanical hearts red, then Grevious can be forced and immobilized - but the Clone Trooper doesn't seem able to shoot him. The Force deflects the shots. So, what are we to do with him?
We've looked for places to throw him against (a la the force option with Super Battle Droids), but no go. Nothing we can force seems to kill him. And, once he's dropped, he's immediately mechanical and, apparently, invincible.