Demonic Spiders: Mostly the demons in the 'Heck' level in the second game, due to being the only enemy who can use projectiles. One does appear in a later level but, luckily, only one. Quite a few can be found in the third game—sometimes they can be easily avoided, and sometimes, not so easily. In addition, they seem to have developed an immunity to knives, must be hit multiple times with the throwing star instead of only once and shoot out fireballs more aggressively.
Goddamn Bats: The frogs (and little bunnies in the first level of the second game). They're too small to hit with your knife unless you catch them in mid-jump and actively pursue you.
Nightmare Fuel: Many of the enemies present in the game will kill Jill in very cruel ways. The traps, of which many will instantly kill her, also do so very painfully and brutally.
Getting killed by a Phoenix will cause Jill to be burnt down to her skeleton, which collapses in a pile of bone dust.
The bees from a bee hive will swarm Jill, repeatedly draining her health, and if she is killed by them she collapses and convulses violently as they sting her to death.
The giant ants are nightmare fuel purely in appearance, and after killing Jill, they will begin to rip apart and feast on her dead body.
The Knight traps will slice Jill bodily in half if she walks past them, killing her instantly.
Falling into a pit of spikes will cause Jill to scream horribly as they impale her in the crotch. Her body will then slowly sink down the spike to the ground as she dies.
Serial Numbers Filed Off: The game was originally based on the Bible, with the main character searching enlightenment. You can see this by opening the third game in a hex editor.
Actually, it was co-developed with Onesimus: A Quest for Freedom, a game based on one of the shortest books of The Bible and published in Christian bookstores.
It's a bit ambiguous, though, how the notes about Onesimus got into Jill 3, as the engine used for Jill was licensed to Ark Multimedia in the middle of the former's development. While most of the graphics and level designs from Jill were recycled into Onesimus (though some text and enemies such as the Demon creatures were replaced), it does seem that Jill was begun first, though, based on release time. While references to Onesimus can be found in the string section and level code of the third Jill game, the end-credits for Onesimus do include a "thanks" to the Epic staff, which suggests that Onesimus was developed simultaneously with Jill of the Jungle 3, and the references in Jill Saves The Prince are a relic of the two development teams comparing notes.