The final boss of The Sewers is Boris, a giant blob of a creature who tanks hits and slides across the map. Understanding how this boss works is the key to beating him and avoiding getting crushed by his body. Here are some helpful tips for beating Boris in Mewgenics.
Boris Boss Guide in Mewgenics

Boris has a ton of health, and every time he takes damage, he moves toward whoever damaged him. This means that if your cat hits him with a melee attack, they will get pushed by him and hurt as well.
Having some ranged attackers can help during this boss fight, such as the Mage and Hunter. Then, when either your Fighter or Tank makes melee hits and gets hurt, you should also have a Cleric to heal them. You get the Cleric collar from Butch after beating Radical Rat for the first time.
Boris has another tricky move called Trample Dash. Only performed on his last turn of each round, Boris will charge into one of four directions, dealing a massive amount of damage to anyone in the way. Avoid this move by making sure that by the end of the round, all of your cats are outside of his trampling range.
You can also stop him from doing this move by freezing him. One of my cats turned him into an ice block, so by the time his last turn came around, he melted and had to skip that turn’s action.
