Guild Wars 2

First off, this idea would require the ability to stow a pet indefinitely.

When a pet is stowed, the player would give a passive stat buff to those around him. The stats that are buffed would be based on the pet that is stowed.

Examples:

Bears: Toughness+Vit
Cats: Precision+Crit Dam%

I and a lot of other dudes wrote the same a long time ago.