Children of Morta

This is the first boss of the game.

It took me a couple of tries so be prepared to not finish it right away.

It only has one direct attack and that is slamming onto you, which is easy enough to dodge if you just keep moving.
Though it becomes more tricky, when the spider starts to shoot webs everywhere, which slow you down enough for you to then need to dodge, instead of just moving around to evade the spider.
Last it summons additional spiders to fight you. Those can be quite annoying and should be dealt with quickly before returning to the Spider King itself.

I beat it by using Linda, since her being able to move and attack at the same time helped me evade the Spider King while shooting the other spiders and the King itself.