Where a fight starts
Battles run from the BATTLE terminal in your base. It offers two entries: CAMPAIGN for stage fights against themed enemy teams, and PVP (THIS SERVER) for a challenge against another player in the same server. Both take a three-creature team, and both are turn-based: you pick one skill per creature, then the enemy answers.
Arena is not a menu. No collected screen shows a separate arena mode. The word shows up on creatures: a Golden shimmer prints ARENA BONUS +50% and a Diamond shimmer prints ARENA BONUS +100%. What that bonus changes in a fight is not explained anywhere collected.
The fourth skill is a level gate. Each creature shows four skill slots, with the last one locked until that creature reaches Lv10. Until then, a fight is decided by three skills per turn plus the three creatures you brought.
Edition warning: arena pages, arena stat tables, and arena-combo videos that rank for “animash arena” describe the standalone mobile game. The Roblox build has its own terminal, its own creatures, and its own mode names.