NOTE: By their very nature of not being canonical/official, and the ginormous amount of unofficial content for each one of these games, game mods are excluded from this list.
Unreal I (includes Expansion Pack Return to Na Pali)
- "Cellars at Dasa Pass": Not only is there a brutal segment where you have to fight a stone titan in a relatively small space, the level has several places (including the aforementioned stone titan fight) where you'll have to deal with endlessly respawning krall pairs (i.e there will be two krall, once you kill them two more will show up, repeat ad infinitum) and, in a bit that seems just plain unfair, right before the exit there will be another respawning krall pair, which most players will probably assume is just like the others and look for another way to open the gate to the exit. However, this respawning pair has a finite number and once you kill enough they stop spawning and the gate opens. The level is a pretty big Guide Dang It! as well, with you spending a lot of time finding a new lever, flipping it, then wandering all over the level trying to figure out what the hell it opened.
- The second visit to the Skaarj spaceship, just before fighting the Queen. This time around, the power has gone out, leaving you fighting nothing but Skaarj with shields and larvae in a cramped environment pitched in complete darkness. It doesn't help at all that, of course, ammo and medkits are extremely rare. If your skills with the dispersion pistol aren't top notch (and if you've skipped upgrades for it to turn it into something worth using), expect to die a lot.
- From Return to Na Pali, the UMS Marine fight. Once Prisoner 849 activates the ship, nine UMS Marines, three at a time will attack you. They either come with the Grenade Launcher, the Rocket Launcher or the CAR. Their damage output is upped for the fight, and no matter where you hide, they will find you, as the elevator to the lower levels is disabled. They also strafe fast, removing their need to dodge, and forcing you to go outside in order to fight them.
- DM-KGalleon (Koos Galleon). It's extremely intricate, with lots of obstacles, it has a lower floor where dodging is difficult, some weapons are in places which are hard to reach, and some passages are extremely narrow. Couple this in single-player with the fact that the "weapon stay" preferences are offnote and that the bots will be more focused on shooting you than their enemies, and you've got a really hard challenge, probably even harder than the final match.
- The console version of the map lacks the lower floor, so it becomes somewhat easy, averting this trope. Of course, when you pair it with the issues mentioned in the UT YMMV page's Porting Disaster entry, well... it becomes again a hard match.
- Due to your teammates being incredibly incompetent and the fact you can't be everywhere at once, any CTF level in single player quickly becomes an irritating hassle.
- CTF-Face (Facing Worlds), one of the first levels of the Capture The Flag ladder, can be this, thanks to the sniping positions of the two bases having an open view of the spawning locations, allowing snipers to spawncamp opponents indefinitely and in near-total safety, and if someone ever manages to live long enough to grab the flag, they'll surely eat a headshot as they try to make it back to base. It's not unknown for there to be no flag captures during regulation time.
- Xan Kriegor on DM-HyperBlast. Not only does the level take place on a small space cruiser where it's very easy to fall off and die, Xan himself can make this utterly and incredibly frustrating, as he'll likely obliterate you the first time you face him, and his favorite weapons can very easily knock you off the ship and into the abyss of space.
- The worst part of it being that Xan likes to hide, making it a violent hide-and-go-seek. And a very fatal one if you fail to constantly look behind you. Made easier by Xan's constant spewing of taunts, though, even if the way the game handles them means you can't use them to locate him.
Unreal II: The Awakening (includes multiplayer-only Expansion Pack XMP)
- The third planet is called "Hell". It's set in a factory on a cold planet. The memorable part? The. Enemies. Are. SPIDERS!!! Tiny ones that attack in groups as they crawl up to you & huge ones that leap across the room at you. To a player who suffers from arachnophobia, they will find themselves in a spot of trouble in Hell.
- The Hold the Line-style levels are quite the annoyance:
- Swamp, the first level after retrieving the first artifact, starts easy and nice, with you taking a walk over the breathtaking swamps of Elara V to rescue a pair of marines. Then you move onto the second holding point and during five minutes you need to hold your own while hordes of Light and Medium Skaarj warriors tear you and your allies a new one. For the record, the clunky movement mechanics of Unreal II play against you while your enemies are faster, retain the leap attack from the original game, and their bolts have a big splash damage. Good thing that Gameplay Ally Immortality is on your side for this mission, otherwise would be a quick Non-Standard Game Over.
- Kalydon, the mission that takes place after the energy-draining Severnaya, requires you to defend the door to the repair station while hordes of Liandri Angels (which also include at least one Rocket Launcher and Flamethrower-armed Heavy Angel per wave) constantly press over you and whatever defence you managed to build. You have four waves with almost no downtime between them. Good luck!
- Due to your teammates being incredibly stupid and the fact you can't be everywhere at once, any CTF level in single player quickly becomes an irritating hassle.
- The fourth level of the single player, DM-1on1-Desolation, is played with 5 bots. The level is small and cramped, with tight corridors because (as its name suggests) it's supposed to be played with two players rather than six, with lots of things in your way such as pillars, narrow passages (which makes them as frag bait when someone shoots with splash damage weapons like the Flak Cannon, the Rocket Launcher or the BioRifle) extremely few options to trickjump, and the only way to get some armor is by using the Booster adrenaline combo with enough health. There's also an UDamage, which the bots will steal if you don't know how to time it well. Oh, and if that wasn't enough, the bots have a tendency of annoying you unless you react quickly.
- The "Bridge of Fate" maps from the Bombing Run and Capture the Flag ladders. Both maps are composed by the two bases separated by an abyss, joined by three very narrow bridges. The CTF match, in particular, makes returning with the flag a chore, even if you take the lateral routes. If you don't have trustworthy teammates covering your back, you're screwed. As for the BR rung, it's a chore for defense and getting the ball, mostly. Since the ball is in the central bridge, you need a good teammate located at the end of one of the lateral bridges so you can pass the ball. However, the AI isn't programmed for tactical positioning, and they'll go directly to the ball, so your best bet is for you to be the better positioned one and expect a bot to pass you the ball... making you the newest target of the enemy team. At least the BR match is switcheable, however...
- ...said alternate map is BR-SkyLine. The map is composed of three towers, the two team ones, and a central one where the ball is located. The layout seems to be pretty straightforward, and in normal game settings there shouldn't be any problem. However, the map itself is low-grav (meaning that Shock and Mini hits have extra punch, and you're more vulnerable for Rocket and Link hits, while your air control is pretty low) and the entrances and exits to the central tower will be harsh, to say the least. Couple that with the goal being located inside of the team towers, most of the team spawns happening inside of this tower, and scoring becomes a hell of a chore.
- There's also the final Assault map, AS-Mothership. You and your team have to infiltrate a Skaarj mothership, including taking out its outer defenses and getting into its tiny entrance bay via spaceship, where you can and will be aggressively shot down from every possible direction before you can retaliate. If you do manage to get inside, you'd think things would get easier once you're on your feet in familiar gameplay territory, right? Wrong. Expect to spend ages respawning over and over again trying to evade the AI's Instant Insta-Kill Rocket Launcher Attacks of Insta-Death long enough to wear down each fanatically guarded node before the timer runs out (and, in the case of the last ones in the control room, even reach them at all). Destroying the reactor core and completing the offense portion is a miracle in and of itself; when the enemy attacks they will be sure to bring their AI of Doom with them, rendering your defenses helpless as they tear through the very defenses they made nigh-impenetrable before. And this is on the easier difficulties.
- The final match, DM-HyperBlast2. It's a widened version of the original, meaning that you need to move a bit more to hunt down whoever is the leader of the best team in the ladder.note Even on the lowest difficulty setting, they will religiously pound your ass. There's a catch, though: since opponents dying to world hazards such as the void count as a kill for you if they flew into it from one of your shots, you can camp the Shock Rifle and Super Shield area, negating both of them to your enemy and getting relatively easy kills.
- Any mission where your team is outnumbered. Any mission where your team gets instant access to the Leviathan and can get stuck. Any mission where your team is both outnumbered and can get stuck in the Leviathan. Now that we got the abridged version out, here's the full detail:
- "Diesel" from Act II: With Caesar's Coin is a 2-on-4 Team Deathmatch match in a small map where you're paired with the worst member of your team against four of Iron Guard's best. Good luck getting the UDamage before they get it. The same can be said for the Biohazard and Deck missions from Act IV: Calculated Losses, except that those are optional missions and you may want to skip them.note
- A very special mention goes for "Torlan Delta" (a.k.a. Torlan_Leviathan) from the end of all but one of the Act II: With Caesar's Coin paths, with your team possessing the Leviathan against the Krall and their two Darkwalkersnote . The game's visual code calls this level an "Invasion-style" match for good reason: it's a completely and unfairly asymmetrical 4-on-7 match where your AI will be at its worst as you see all of your companions getting onto the Leviathan and making useless attempts at taking the nodes and the enemy base. Your only choice can be getting the Leviathan as soon as it spawns and deploy as close as you can between the objectives. It's on this scenario that you may want to play the Iron Guard Reinforcements or Tactical Diversion card if you have them. You WILL need them.
- "Dusk" from the beginning of Act III: The Liandri Conflict is a 4-on-6 Warfare match that requires you to NOT to be distracted with the Support Nodes (which just gives you access to the Cicada and the Shield Belt) and get to the enemy core and destroy it ASAP. Should you fail to do so, you'll be overwhelmed with hordes of Liandri Bots not giving you the chance to retaliate and attacking you from anywhere.
- Also from Act IV: Calculated Losses is the "Onyx Coast" mission. It should be easy. Pick the Leviathan and start busting enemy nodes with your teammates covering your ass and doing the node building, isn't it? Well, no. Your enemy start with two Darkwalkers which are slightly weaker but faster than your beast, and have numbers advantage (4-to-5). Add to it the dumb Leviathan AI already mentioned and you'll find yourself not being able to be anywhere while your teammates are stuck in the Levi and your enemies keep charging against your core.
- Act IV: Calculated Losses starts with "Islander Necris". Remember the Islander level where you get a big bunch of Axon vehicles and your enemy only a pair of turrets alongside barricades placed in order to prevent vehicle invasion? Well, you start on the Turret side, and your enemy starts with a full array of Necris vehicles. If you cannot get the Orb to the Prime node and start busting the enemy core, you will suffer. A lot.