* CompleteMonster:
** Conda Challis. During his appearance as the notional villain of ''Orphan Star'', he displays a truly legendary capacity for depravity. Among other things, he attempts to recruit Flinx to create memory-plays in the Janus Jewels, and the "scenes" he wants to see turn the stomach of even a hardened StreetUrchin like Flinx. He loves torture as well, but the best example is what he plans to do with his "adopted daughter", Mahnahmi -- raise her to maturity and then use her as a sex slave. It turns out that he was being telepathically manipulated by her much of the time, simply to keep him functional as a human being rather than descending into a vile pit of vice, which triggers his VillainousBreakdown when he discovers the fact.
** Lord Dominic Estes Rose, a major villain in ''Bloodhype'', is a drug dealer who trades in substances other dealers won't even touch, like the titular bloodhype. Like Challis, he enjoys torture, and responds to news of the escape of a set of captives by crushing some songbirds in a cage. He then attempts to blackmail the [=AAnn=] on Repler by threatening to release his stash of bloodhype in their compound, horribly killing all of them, and manages to provoke the [=AAnn=] commander into declaring him the most disgusting being he's ever seen. His hubris reaches its pinnacle when he attempts to [[DealWithTheDevil sell humanity out]] to [[EldritchAbomination the Vom]] in exchange for his survival, [[EvilIsNotAToy and promptly dies]].
* InferredHolocaust: Better hope nobody lives in the universe which [[spoiler: Flinx dumped the Great Evil into at the end of ''Flinx Transcendent'']]. Also, once [[spoiler: the Great Evil]] has been dealt with, what will happen if [[spoiler: the Xunca decide it's safe to return to their original galaxy and kick out the squatters?]]
** {{Jossed}} on the first point: [[spoiler: The Great Evil is evil [[OutsideContextVillain because it is not native this universe and so unnatural.]] Back in its own natural universe, it will not cause the same problems.]]
* NightmareFuel:
** Any time the effects of Pip's venom are described in detail. EyeScream only begins to cover it.
** There's a particularly memorable scene in ''Bloodhype'' when Dominic Rose crushes some exotic birds in a cage, plus the description of the effects of the drug itself.
** Conda Challis' nasty little perversions in ''Orphan Star'' -- although this is given something of a GoryDiscretionShot by only describing Flinx's reaction to (and Challis' pleasure from) them.
** The planet of Midworld could be considered NightmareFuel incarnate given the enormously varied and nasty ways the plant life has to kill people.
** There's a scene in ''Trouble Magnet'' when a part of the StreetUrchin gang are tortured by having thousands of sharp pointy metal objects pinned to them via magnets.
* TheWoobie: Flinx's alienation from the rest of humanity is played for all the {{Wangst}} that it's worth and then some, especially in the later novels. At times he crosses into SympatheticSue territory.