Here's a not-entirely-finished answer.
An RPG character that's a member of a race like the Pandaren (WoW) or Baraka (TERA)
I am always on someone's cam,
He controlls the way I am.
"cam" meaning computer monitor. The player controls the character using this.
I am tall,
And I listen to mall,
I am very fat,
Unlike a bat.
These are tall and fat races. There's either a bat-like character or enemy that's thinner. For reference, Googling for bat with the RPG name gives a comparatively thin-looking giant bat for WoW.
"listen to mall" probably refers to some NPC or god named "Mall" or similar that the character follows. Nothing comes up in searches so far, though.
I can light a fuse,
I can gather food,
Or chop down wood,
I can mine,
Standard MMORPG actions
Or cut through slime,
Basic MMORPG encounter
I can build,
Or sell to a guild.
More standard MMORPG actions
You can change my look for fame,
But my sizes will remain the same.
Equipment gives bonuses, is vital to progressing in these games and is the main customization point of a character. However, the underlying character shape is pretty much invariant.
I haven't played an MMORPG in ages, and I've never played the ones mentioned here.