Mokona
Mokona is a marshmellow look-alike seijyuu, or holy beast, that accompanies the Magic Knights in their quest. It provides everything that they needs, including food, water and shelter from the gem on its head. Mokona also tends to hide or run to some place safe when the knights are fighting either against monsters or against warriors sent by Zagato.
Mokona also enables Fuu and Umi to communicate to Clef near Lake Eteruna when they confronts Alcione and she starts to attack them with her magic. It lets the girls to have their magic adknowleged and use their powers to stop Alcione.
Of all of the three Magic Knights, it gets along the best with HIkaru and the poor Mokona always trys to run away from Umi whenever she gets into a fit and starts to chase it around (you will probably get frustrated too if you talk to someone and the only vocabulary he/she knows is "Puu")!
In MKR 2, Mokona returns and it's real indentity is revealed.