Okay, I honestly, it's just my opinion, but personally I find regeneration is the worse pet to fight, it's like one moment you think you are gonna win, then BAM, the pet suddenly makes a startling comeback and tosses you right out of the arena. Most of the time, my pets are good, I don't really train bad pets, but the problem is, I can't always beat a regeneration pet.

and also, I think the arena should be less buffed up, it's too OP right now, I mean seriously, five level difference? Sometimes it can be dead obvious who will lose and win, if you got a level 30 pet on autobattle, then obviously a level 35 has the higher chance of knocking the pet right out.

but ok, at the same time, genetic power, so hard to fight against, one of the worst pet fight I ever had was against a regen genetic power unicorn..but yeah, anything under level 35 in the battle arena is somewhat easier to fight, anything above, that is when so many genetic power pets come running in....yikes

ok, enough rant but for best combo, I think for gryphon is an active berserker and gladiator is rather OP, for puma I'd say second breath and silent pace, fighting against one...eeps...for unicorns, diamond horn and regen is rather hard to fight combo, as well as regeneration and determined. For cockatrice I think the best combo is bet expert and regen, as well as acid gland and splitting muscle. For dragons, I'd say boiling blood and robust scales, I had trouble trying to take one down,lol. For roc, Musial beak and sharp feathers, these are just my opinions.

The level difference doesn't bother to me, I'd rather prefer to separate the GP pets by levels, 5 levels between a GP 1 and another GP 1 is nothing, but a GP 1 pet vs a GP 3 pet with higher level is almost impossible to beat (Almost, because my unicorn Queen of Hearts is GP 1 and has defeated many lvl 50 GP 3 pets)

About the best combo, I've only studied it for unicorns and I'm breeding to achieve it. My goal is to have magic horn, quickming, agile claw, regeneration, fragance and gracefulness (I only need magic horn dominant to achieve it)

If you get a unicorn with that genetic combinations without GP, it could easily defeat a GP 3 unicorn of the same level (If it doesn't have many genetic boosts)

I've came close though...minus magic mirror though..