These units deal 2.5x damage against Behemoth Enemies, take 0.6x damage from Behemoths and have a set chance to dodge their attacks.Cats only gain Behemoth Slayer after true form or through talents.
What are Behemoths?
Behemoth Enemies are a type of enemy introduced in version 11.5 and chiefly encountered in the Behemoth Culling stages, Zero Legends and the Zombie Outbreaks of Cats of the Cosmos Chapter 2. Behemoths tend to have at least one immunity (most commonly to Surges), very high combat stats compared to most normal enemies, and certain attack-related abilities such as Long Distance, Omni Strike, or multi-hit.
Source: https://battle-cats.fandom.com/wiki/Category:Behemoth_Enemies
What Behemoth Slayers should I get?
Firstly,you should get Val Val Cat because of its evolution cost,needing only one red Behemoth stone,three red Catfruit and three red Catfruit Seeds and its 100% chance of performing a wave attack.
Next,after beating 5 Behemoth culling stages,visit the catnip missions to get Ancient Egg:N101.True form it with 5 purple Behemoth stones and 5 red Behemoth stones to get Courier Cat,after which you can forget about Val Val Cat as Courier Cat outclasses it in every way possible.
List of Behemoth Slayers: https://battle-cats.fandom.com/wiki/Category:Behemoth_Slayer_Cats