The first one could be a great monster to fight in a jprg set in a school like the shin megami tensei games.
The second has the least exaggerated and more uniform desing, I can see this as creature you see in subnautica.
The thrid one reminds me a lot of the final boss of illbleed, not much of a fan of the composition but I feel like with two, maybe three things you tweak this desing could turn very solid.