When bosses fuse... you get fusions When they fuse together... you get grand fusions Here's how they work: 19 (9+10): they move like 9 but have a timer like 10. 30 (9+10+11): they move like 9 when hidden and show themselves from time to time, once fully revealed they will place a flag, click on them before they materialise to stop them and reset the timer if it's within 10 seconds or less (the timer halts when placing a flag). 42 (9+10+11+12): the answer to life the universe and everything, they currently look like this as we don't know how 12 looks (will update when ep. 4 is out).
I think I should explain Better: these are the grand fusions because they are fusions of each version of MS+'s bosses(v2.0 Is 9 and 10, v3.0 Is 9, 10 and 11 and so on)