This one's kind of fun. In Final Fantasy 6 for the SNES (otherwise known as Final Fantasy 3 in North America) there's a couple of bugs that will let you defeat just about any enemy or group of enemies with essentially no effort.

First, get into battle with a party that has Cyan in it. Then have him charge up his SwdTech to level 2 (Retort).

Then, before he has a chance to use it (i.e. before he gets hit with a physical attack) turn him into an Imp.

Then kill him off with a magical attack.

Then revive him.

Now the fun begins.

As soon as a physical attack is made, from anyone to anyone else, Cyan will counter it.

And, because of a couple of bugs, he'll continue to counterattack until every enemy on the screen is dead.

You might run into a problem if an enemy on the screen is invisible or otherwise can't die from physical attacks, so be careful. Once this bug is initiated, you can't do anything else until the battle is over.