Korgoth said:
You are going to face some high level minions, like a legion devil. So you get yourself a zombie minion (you either create one to serve you, or you just go on a zombie roundup and hogtie the thing). So you have a zombie minion in the square next to you (still hogtied, perhaps) when the netherworldly minion (or whatever minion) steps up to rumble. You then use Cleave on the hapless AC 13 zombie and instantly slay the mega-minion.
If I had a player pull this in a game, two things would happen:
1 - I would congratulate him on his careful reading of the rules and his ability to come up with a combo like this. My players usually don't get that tactical, so it would be worth a hearty "attaboy tiger".
2 - I'd ask him to tell me how he's going to tell a minion Legion Devil from a non-minion Legion Devil to know when his trick is going to work and when it's going to get him squashed by a non-minion.
3 - If he tells me that all Legion Devils in the Monster Manual are minions (don't know if that's true or not, but if it is), I'll just smile and point to the section on "building your own creatures."
You can't look at a minion and go "oh, that's a minion". Well, you CAN, but it's only because the DM has specifically allowed you to believe it's a minion. On top of that, minions are either supposed to go down easy (for dramatic effect) OR dogpile you and give you a challenge against overwhelming numbers. Because of that the minion killing Cleave attack outlined here is mostly useless except as a "let's see how far we can bend the rules" construct. If minions are going down like Nazis in an Indiana Jones movie, then you don't need anything as elaborate as a Zombie Cleave to take them out. OTOH, if they're coming at you in massive numbers to overwhelm you, then the Zombie Cleave is going to be little more than a nuisance to them.
The only way this combo would be of any use at all is if you had some low-level characters who were attempting to take on a challenge much higher than their level - and the books apparently warn you that you're supposed to use minions scaled to the appropriate "threat level" of the party. I would read that to mean that until the party reaches an appropriate level, those Legion Devils guarding the Gates of Hell are not minions at all and don't go down on one hit - it's only once the party passes a certain level of expertise that the Legion Devils become a minion to them.
(I would also not allow a helpless target to count for the Cleave power at my table - but that's probably a style preference and not specifically outlined in the rules - so the Zombie would have to be untied and able to physically attack the character in question before I'd allow Cleave to be used anyway).