I think the first thing u do is evol it ... coz it still gen1 pet and lv is 6x to keep upgrade stat ...
For the sphere location, shadow C, Mayor Flynn, Sea Serpent, Demiguise, Garm, all light dragon stage and ... i still dont know ... personally reccommend Mayor Flynn ... coz easy to beat at low lv or Demiguise ... coz drop Alieneye (one of the most useful healing pet)
For the upgraded stat, I dont know coz i ever never want to use this pet due to the ugly looking ... 555
But I see many ppl use it as tank and stun opp pet and the stun combo skill ... so should put att and def depend on your plan to use it ...