This enemy dies once after attacking, but has a 100% chance to slow cats for 10 seconds and a 100% chance to knockback cats along with an Omni Strike attack that can reach up to 125 maximum range. It has almost a million health and immunities to most debuffs, meaning it will almost always be able to attack your cats, causing them to be applied with deadly effects.
Don't bother trying to kill this enemy. Instead, bait his attacks with something along the lines of Tank Cat so he doesn't hit your important units. Alternatively, you can use slow and knockback immune units to ignore its effect on the battlefield completely, or you can use units who only resist/are immune to slow and take advantage of Wafer Cat BIG's knockback to ensure their safety.