Thank you for playing and glad you enjoyed it!
As for the boss fight, one of the NPCs mentions that werewolves can't be affected by the same attack twice. This is a small hint that you have to successfully hit them once with each character in order to succeed. The red orb indicated that he took damage from Oomp's Fireball, and the green cirlce indicated he took damage from Sloom's melee attack. You still needed to hit him successfully with one of Seraphina's arrows in order to defeat him.
As for him vanishing, were you close to the edge of the screen? It's possible that he teleported behind you and ended up one scene back and due to his VisibiltyEnabler2D, his process turns off when he's off screen, but going back one scene should have kicked it back it to where he teleported back to one of his other three teleport points. I might have to put an exception in the script to make his process keep going even if he teleports off screen when this happens. Thank you for reporting it! I would love for you to give it another try and see if you can get through to it again!
Thanks again for playing and commenting!