The Metal Slime isn't a character that is supposed to be defeated easily. First off I'd have to say don't use magic; it doesn't work against them. Next survey the situation; is it just one Metal Slime or a group of them? Is there other enemies? Depending on how strong you are is what you will do. If you are weak take care of the other enemies first, this may provoke the Metal Slime to run but that's better than being dead. Next just press the ATTACK button until Metal Slime flee or die. If your life gets low have Cristo Heal. If you are stronger keep the other enemies there but hamper their abilities this will make the Metal Slime more comfortable (they may still flee). Equipmentwise I'd say you need Meteorite Armbands because it's either hit or miss; whenever you hit and get a terrific blow the Metal Slime is dead, but a normal hit will take 3-4 more hit or miss processes to kill.
Rom Tip Save the state as soon and you see the Metal Slime then Follow procedures above. If the Metal Slime flee restore the state if not then save the state again.
Whenever going into the tournament don't get the mirror of ra. It justs waists a turn you could have guessed where he is. Save up your Medical Herbs throughout the tournament you might need more here than the others. Just keep guessing where he is and use a Medical Herb if you are low in life. Watch what he is doing; if he builds up power it may be a good idea to PARRY until he attacks.
Rom TipLocated in the Tips section
What makes the Chameleon Humanoid hard isn't himself or the two Rabid Hounds beside himself; it's the fact that either you don't have the right equipment of else you don't have a high enough level. If you are able to buy the best equipment for everybody you shouldn't have to worry about your level either. a spell that comes in handy in that battle is Upper. Have Cristo cast it on the weak then working your way up to the strongest, after that repeat. Another way you can tell if you are ready is if you can defeat a Rabid Hound in one round, ie. Alena attacks and Brey casts Icebolt then a Rabid hound is dead. If you can do this you can take out Chameleon Humanoid's henchman in two-three rounds. Finally focus on him.