Overview
Boris is the boss of The Sewers, described as a grotesquely bloated cat. Despite having 200 HP and 0 base attack damage, Boris is deceptively dangerous thanks to his permanent Trample status effect and four turns per round. He automatically moves one tile toward whatever last damaged him, and his primary attack is a Trample Dash that charges in a cardinal direction until hitting a wall or object, dealing damage and knockback to anything in his path.
Key Mechanics
Trample and Pursuit
Boris has permanent Trample and takes four turns per round. After being damaged, he automatically moves one tile toward the source. On his final turn each round, he attempts a Trample Dash before moving. If no targets are in range, he simply moves and ends his turn. The core danger is that Boris crushes your cats underfoot rather than attacking conventionally.
Trample Dash
Boris charges in a straight line (cardinal direction) until hitting a wall or object, damaging and knocking back any unit in his path. If your cats are lined up in his charge path, multiple cats take hits from a single dash.
Strategy
The optimal strategy is to spread your team to the edges of the arena. Since Boris always shuffles toward whoever last hit him, a spread formation forces him to waste turns moving back and forth between corners. Alternate which cat attacks him each round to keep him confused and burning movement.
Immobile, Stun, and Sleep are extremely powerful against Boris because they disable his movement, which is his only form of damage. A single well-timed stun can waste all four of his turns in a round.
Tanks with high Constitution can absorb Trample hits more safely. Thieves with high Speed can dodge his charges. Damage-over-time effects like poison and bleed are valuable because they chip his HP without triggering his pursuit mechanic (he only moves toward the source of direct attacks).
Knockback abilities are also useful for preventing trampling by pushing Boris away before he can complete a charge. If you have a cat with Trample immunity, they can trivialize most of his damage output.
Drops
Boris drops random Sewers loot on defeat. Clearing him opens the path to later zones, completing the Sewers branch.