Arcanine or Volcarona?

[Mimifukyu]

I need a fire type for my team. I think i'm going with Volcarona but i just want to see if this is the right choice as i have little knowledge about competitive battles.

My Team:

Cloyster @ Focus Sash
Mimikyu @ Ghostinium Z 
Tapu Koko @ Electric Seed 
Garchomp @ Life Orb
Mega-Metagross

[croissant]

@Mimifukyu I'll assume this is for singles/smogon since you do have a mega evolution and pokébank pokémon which are not allowed in vgc, but please specify it next time.

Volcarona is definitely better than Arcanine in singles, however i do not think it fits this team, since it has a 4x weakness to stealth rock and this team doesnt pack defog/rapid spin, unless cloyster has rapid spin but even then its not even that good at spinning. If you would like more help, i suggest you make a full rmt as i'll be able to help more since what you have could have some potential. If you choose to do so, please take time to read the rules of the competitive discussion forums.

[Marcusube]

Is this team for Singles or Doubles and are you playing by Smogon rules or on Battlespot?

Your post is too vague for me to give you a suitable answer