Fighting a seed team in the Real McCoy tournament, I figured what the heck, I'm not exactly in danger of losing the fight, let's throw out an MB. It lands on a tile with only one other blue in the area, but at the top edge of the screen. The turn before it resolves, I make a match below it so it drops down and now all four tiles can resolve. This is basically the best possible way for Mutagenic Breakthrough to land.
Result: The countdown's new position is diagonal to a team-up tile, which can't be converted, so I only get three special tiles instead of four. When the countdown disappears, a blue tile falls into the vacated space above it, instantly matching the two strike tiles created on that row. The next turn, the AI matches the remaining attack tile. Net effect: I pay 8 AP for a free blue match (which triggered Espionage, hooray?) and one turn of a 44 power Attack tile. Best power ever.
Yes, yes, Hank, I'm as surprised as you are. High-five!
Until they fix his blue, I vote for his best build to be 3/5/5, the reason is, you have a better chance of doing max damage and get max heal and shield with the CD tile Mutagenic Breakthourgh creates then you do after the skill resolves, so you may as well have that CD timer as long as possible, because it's more useful at that point.
Beast is a trash bag. We can debate his uses all day but at the end 2* chars still blow him away.