Which level were you on, was it the boss level or a standard level? Sorry about that, for the time being I would recommend playing on Normal as its the one I tested the most and it should work properly for you.
Lake serpent or the flame drake? I’m guessing serpent since something seems to be borked about him. I know the flame drake works so in the meantime I would try starting a new game and make sure you get the little boss on the map. Restart game until he shows up since its a 50/50 chance until I get it fixed.