Mutualistic relationships

Mutualistic relationships:

(Riddick 3 Concept Art)

I want to use the example of a domesticated animal like a human to a dog rather than a relationship like clown fish and coral as it is far more likely to be the kind of relationship design that would occur in games.

In video game animal accomplices often take many forms, they are a character like any other npc that the player interacts with. giving a steed or pet in a game its own distinct personality or mood is an important part of creating the connection or bond between the player and the npc, visuals play a strong role in this, as well as perceived shared experience.
some examples of the roles that "creatures" play in games, other than enemies:

Familiars:
These are a concept taken from european folklore, ther were believed to be a spirrit in the guise of an animal that practicers of "witchcraft" used to assist in their practice.

These can take various forms, though there are the obvious ones, like a witches cat:

or rat...

steeds- can be animals that the player often develops a bond to/ connection with

Legend of Zelda (Link and Epona)

Shadow of the Colossus (Wander and Agro)

Um... no. Bad example

pets

servants/ minions:

The rats are a fitting animal to use to the character of Dishonored because they suit the feel/mood of the game's environment.