Avatar is the central representation of player influence.
1.Minions and pets follow the avatar and teleport with him.
2.Avatars of players require minimum interactive range to initiate trade/dialogue.

3.Avatars can have cosmetic(display/neutral/town) and combat(pve/PvP) appearance switched by player being in specific zone or by upgrade.
4.Players want their avatar to resemble a specific set of features that they associate with imagined character, customizing their avatar towards that goal. (Restricting avatar customization in favor of realism and aesthetic of game world, will limit immersion)

5.Avatar visual size:such as width/height has to align with hitbox in game, consequently avatars need to have a minimum visual size high enough to occupy the hitbox.
6.Avatar movement/attack speed needs to look realistic at all speeds: stacked +speed/+attackspeed modifiers may force game engine to drop frames with long animations.
7.Avatar rendering cost: diversity of displayed effects/auras/buffs and general amount of combinations of visual equipment create a high graphical cost. (Usually number of rendered avatars can be limited and rendering quality decreased, e.g. only 20 nearest of 300 avatars rendered fully, rest appear as generic class-specific sprite).

8.Avatars need interactive emotions/poses for roleplaying: versatile scripted movement and wide variety of interactions with other avatars, enrich immersion(esp. in social/casual/roleplay-centric RPGs). Stances,Emotes, Poses, Gestures, Animated sequences should be allowed to be set on macro to allow players to create/replay combinations.
9.VR support: For social RPGs, body tracking and haptics may provide much better immersion vs scripted sequences, though it might require player skill and effort to roleplay properly.
10.Avatars as machinima pieces: Custom roleplaying scenarios may require automating avatar movement and action, usually by external program given control of the game. Diversity of interaction and emotes/poses is critical for this use of avatars.