I would just like to put this out there: metal arena has horrible rules. Here's why:
We can only use metal dragons, and they're boosted. That's actually the most stupid thing I've ever seen in the Arenas. I take my time breeding, feeding, training and getting an Apocalypse dragon to A+, and the only dragons I can actually use are my Forge and Millennium. And every dragon, may I add, the only ones allowed to participate, are boosted? That's like saying "only Americans can enter the race. However, all Americans get extra prizes!" Not only that, but METAL. IS. AWFUL. Weak to two of the most common elements, and only strong against terra and some other element, I forgot since I never use metal. Seriously. I can understand banning pures before primals were a thing, and not allowing heroics in lower leagues, but forcing people to use awful dragons, when they've spent lots of time (and sometimes money) training better dragons? They've changed arena rules before, they should really, and I mean really, do it again.
(sort of a vent since I've been forced to use a gold dragon I've named "Worthless" for the past 3 days...)

I feel your pain, only I had 3 metal heroic dragons

Metal arena II you can't use heroics, but can use whatever else and metal attacks are boosted, and every arena above metal is the same way, only able to use that arena's element and having it boosted, and the second part banning heroics and still boosting the element. Just wait till you get to the light arena, where you can only use light and have both light HP and attack boosted.

The purpose of the arenas is to make dragon combat more diverse, so you'll be using dragons that you wouldn't use in normal situations. Don't worry about your Apocalypse, he will have the chance to fight in the dark and light arenas.
As for the metal arenas, try your luck with one of these dragons: forge, millenium, unity, supersonic, magma, bomber, black magic, alloy or electrostatic. The first three can even be bred in the sanctuary, if you don't have them yet.

@Bruno-Pedron Supersonic can be bred too, also Electrostatic is kinda bad because it's a category 7

@bathtubdoritos I know how you feel,having just been promoted into meatle 2(what a relivef)!
The light arena will be easyer for me as I have high reborn,freindship and bolder dragon who would make a good team and I alos have some lv.15s like pinata dragon who are decent in elements.
Hopefully metal 2 will be easier for you as metal gets a atack boost but heroics are banned.