Since its supposed to be a pet and minion class, i think it would be perfect to have 4 minor elementals spawn from the charge bar between 1-99% (Since at 100% you summon the big guy
at 10%: Summon a Lesser Earth Element to crush your foes! (has high health regen and high defensive stats, should have a good single target ability for decent dmg, and if possible to create such as skills, a Taunt ability)
at 25%: Summon a Lesser Air Elemental to aid you and your minions! (Can cast some minor speed/armor/dmg buff for minions like 10% and also do minor dmg)
at 50%: Summon a Lesser Water Elemental to aid you in your battles! (Can cast Healing spells on your character, and a AoE Healing spell which effects your pet and minions aswell and also buff you with perhaps some defensive buffs such as +500 all armor or something else)
at 80%: Summon a Lesser Fire Elemental to devastate your foes! (Can cast Fire Pillars! and Rain of Fire + some decent Single Target Ability)
They should last untill they die so you dont have to keep the charge bar at 100% all the time. Could also be a passive skill which unlocks the 1-4 lesser elementals summoned from chargebar at 5-15 points invested.