Lineage 2 expansion, Hellbound, is currently in test, and with its improvements and new content come changes to the pet system that fans will love. For example, people who have wolves as pets will be able to evolve it to a mountable form called a Fenrir. This change isn't merely cosmetic -- it will get special attacks and more powerful skills, and also confers its power to its owner while mounted. Clan members have further customization available to them, able to upgrade their wolves to Great Snow Wolves, Red Striders, and Snow Fenrirs.
For the other pets, the level caps have been raised to 85, concomitant with players' level caps. Once the Baby Buffalo, Baby Kookaburra, and Baby Cougar pets have exceeded level 55, they, too, can evolve into more powerful forms. Each one is geared toward a particular class, and grants buffs accordingly.
Visit the Lineage 2 site for more information, and check out these evolved pet screenshots!