Mercury healing and mako slow imun?
That means slow immunity for Makos and HP regeneration for Mercurys.
4 HP per second would be a good ammount. (300 HP total)
(im compare Demeter have 60 regen per second and 6000 HP, Vulture 1000 regen and 100k HP, Zeus 10k regen and 1400k HP)
That wouldn't make a big change, but improve the game logic. (easier to understand)
Addition:
To fulfill the setting complete Mantas would need at least a little HP boost to?
actual they have 3500 HP What about 3800-4000? That would give everyone more tactics to overcome red splashes.