It has extremely short ranged attacks, but makes up for it with the ability to spawn level 3 Wave Attack at a 100% chance. Treat him as a stronger Kory with less standing range that spawns in mass. Do note that he Crazed Gross's Wave Attack reaches a range of 800, meaning only a few cats like Nerd Cat can avoid the attack.
Alternatively, you must avoid meatshields and use plenty of ranged attackers, such as Dragon Cat or Paris Cat, as these will eventually stack up and knock this enemy back before it can even attack.
If you have Awakened Bahamut cat this stage would be easy for you. Also he can be killed while he is attacking the base so, if you have any wave blocker units bring them in your team and protect him at all costs until the base is destroyed.