This video demonstrates defeating Katash at the top of White Towers.
vvvvvv [See Below for Explanations] vvvvvv
Katash is perhaps one of the biggest difficulty spike in this game, with fast attacks, small hitbox and decent defense. The most efficient way is to exploit his certain attacks to deal massive damage, as opposed to chasing him and only chipping away his HP slowly with ranged attacks.
Katash cycles between 3 attacks in the first phrase:
0:17 Triple Dash, pay attention to the audio clue and jump accordingly
* Attack opportunity: Aerial*3 + Charge + Aerial = 66 DMG (16%), or 81 DMG (20%) with boost
0:12 Blaster Pellet, try staying behind him
0:07 Blaster Missile, walk underneath him and time when to fire the Crossbow straight up
When his HP reaches around 50%, he enters the second phrase with 3 more attacks:
0:45 Swipe, drop back to the placed Spear before he attacks
0:52 Spaceship Laser, jump onto the spear near Katash
* Attack opportunity: Knock him down with Tusk Strike or Charge Swing to deal extra 99 DMG (25%)
:- Mole Mines Summon, you may dispatch them with Charge Swing + Tusk Strike
It's worth noting that if Katash steal "Food" from you twice, he would be poisoned and gradually has his HP reduced. However, this is not recommended because you will first need to be hit by his dash attack twice.
Good luck!