With 200,000 health at base strength magnification, Ovis is the tanker of the Pokopang group, and at his strongest (Rainbow Blast! at 3 crown difficulty), he'll have 400,000 health. Additionally, he only has one knockback.
There is not much one can do to Ovis besides deplete his enormous health pool with many attackers. Hip Hop Cat's range is on par with Ovis' and can always take at least the very first hit from him if his True Form has been unlocked. Fencer Cat would be complementary to Hip Hop because he can outrange Ovis and still do some good damage. But if Ovis is with other Pokopang members, such as Pokota and/or Coco, Crazed Bahamut Cat should also be present to keep them at bay.