Anybody remember my old picture of these? [link] Aside from looking dreadful I'd taken some artistic liberty with Cloaker's design since I couldn't really make out what was going on with his sprite. Since finding official artwork of him I've realised he's supposed to be a bottle. Maybe to make a genie connection or something? Perhaps Cloaker is the bottle, the physical aspect and so a physical fighter and Domino is the genie, the magical being and so a magical fighter.
As you might recall when you destroy one of them the other will run away and connect to a large snake whose identity and abilities depend upon which character fused with it. But what if you destroy them both at the same time?
Well Cloaker is weak to magic and Domino is weak to physical attacks, but the only moves in the game that can hit more than one target are magical attacks. I did the experiment by whittling Domino's health down to 1 and Cloaker's down to a couple of hundred before using a magical attack. The result? Domino took no damage at all. So there you go, it's impossible to destroy both at the same time.
I remember getting into an argument with my significant other weather Cloaker had a beard or giant, gnashing teeth. It's really the only "real" argument we've ever had and it continues to this day. Fun times. You did a good job depicting these two, what with not much official artwork for Mario RPG for reference.