PvP arena is a level specifically designed for PvP;
1.Symmetry: Map should have bilateral or radial symmetry, starting spawn points should not influence gameplay.
2.No Monsters:monsters shouldn't influence combat.
3.No loot(treasures) or player-loot(body looting. In arena map, PvP is civilized):
all players start and leave with same equip.
4.Instanced-only:in-world laws may amended to provide balanced combat.
5.Once player dies, he exits the arena. No respawns, instance ends with last team/player winning by combat.
6.Specific skills or spells may be disabled or nerfed for PvP;Teleportation, Area-of-Effect skills, powerful slow/critical strike modifiers, etc. Balance > Realism.

A. Duel Arena(2p total). Instanced PvP area is ideal, without spectators to reduce lag.
B.Team Arena(2p+ for each team,N players per side).
Instanced PvP area with spectators.
C.FreeForAll/BattleRoyale. (N players battle until one left).
Usually harder to balance, carefully check that spawn points don't provide terrain advantages or any shortcut to important area.