I'm digging the idea of werewolves and bloodmoons, the ghost mobs might be doable because there is a mob that does that naturally in the game that I can copy code from.
An interesting concept, I would consider it, maybe what I could do is biome specific creepers, like desert creeper is beige colored instead of green. etc
Perhaps, basically I would have to write a new entity class and then either take the model for a creeper and resize it somehow or draw an entirely new model, or part pick from an existing model like the creeper to make the creer. I'm gonna try forsure
Could be interesting, might give some mobs ability to attack with lightning, maybe a chance that some skeletons spawn that shoot, poison, lightning, fire, blindness arrows
The mod i wrote already has alot of that kinda. Mobs are faster, healthier and more deadly. I don't have the spiders spitting cob webs thing but I think I know what your talking about.
Technically the mod locks the game in a 4th difficulty called "Nightmare Mode"