For battles with front and back hero rows. Do not apply the same figures directly to march combat.
When do they open?
Hopper opens from server week 17; Chompy from week 19. If they have just appeared, check your server week and their availability in the pet screen.
When your front row struggles below half HP
Hopper reduces incoming normal-attack damage below 50% HP. Consider it with Nikola or Lava when you want them to survive that range. The opening attack and dodge buff goes to two random allies, so you cannot count on a particular front-row hero receiving it.
Lava changes between an auto-attack boost and healing around 50% HP. Choose between Hopper for surviving the low-HP range and Fluffy for more healing by looking at the rest of your lineup.
Does Chompy fit a critical lineup?
Chompy targets the enemy with the lowest HP in its opening attack. It also adds critical stat to your heroes, making it a candidate for Becca, Chiron or Alita lineups that use critical hits and finishing damage. A critical stat increase of 30 does not mean 30% critical chance.
When should you consider the other pets?
Check whether your front or back row needs help. Random targets, the nearest target and the whole lineup are different scopes.

Snowball
Early attack support, with more attack against enemies below 25% HP.

Dodo
The opening attack buff affects two random heroes. Also has feeding and hatching effects.

Buckler
Protects the one nearest ally. Check the distance to the hero you want to protect.

Fluffy
Adds sustained front-row healing, lineup HP and healing effectiveness.

Ironhead
Boosts front-row attack and reduces the nearest enemy’s defense.

Shadow
Adds attack against enemies below 35% HP. The opening mark targets a random enemy.

Snowy
Reduces enemy front-row attack and attack speed; adds attack and defense after a kill.

Starhorn
Adds front-row defense and back-row attack for the first 10 seconds.

Chompy
Targets the lowest-HP enemy and adds critical stat to the lineup.

Hopper
Reduces normal-attack damage below 50% HP. The opening buff affects two random allies.
Do locked skills count?
The second skill opens at training stage 2, the third at stage 4 and the fourth at stage 5. The first skill has six levels; each other skill has one. Count only the skills your pet has unlocked.
Keep increases to the pet’s own stats separate from hero stats. Dodo and Buckler’s feeding and hatching effects do not strengthen a particular hero in combat.