History VideoGame / XComTerrorFromTheDeep

* ObviousBeta: Terror From the Deep was made by recycling a large part of the coding for the previous game which, although saved some time and money on development, meant that some serious and inherent issues would crop up during a playthrough.
** It has a lot of crippling bugs. Xcomutil patched most of them, but you get goofy stuff like soldiers disappearing on 2-step missions if they get knocked out, base missions where you can't find the last alien, and the "Tasoth commander bug".
** Additionally, there are nonsense impediments to some of the important research tree, which lead to more bugs, which aren't game-ending but still make the game needlessly more difficult and time consuming. You need a live Deep One to research Ion Armor (the equivalent of the Power Suit from the original game), so if you roll unlucky and aren't aggressive enough, you may not see ion armor (and subs) until very late in the game since Gillmen quit running terror missions after a couple months.
** The "Updated Pathfinding AI" in [=OpenTFTD=] should make the Cruise Missions etc. a bit less tedious. Warboy discovered that the original algorithm wouldn't let aliens make two 90 degree turns, so that's why the game had so many "closet campers."
** Converting the unlimited-ammo Laser weapons to limited-ammo Gauss weapons led to a very annoying program oversight with the Gauss Coleacanth.
-->The Coelacanth/Gauss does NOT return any remaining ammo to your stores at the end of a mission. In addition, when you assign a Coelacanth/Gauss to a troop transport, 50 Craft Gauss Cannon rounds will be immediately deducted. These rounds cannot be refunded by any means. If you change your mind about assigning it, deassign it, and then reassign it, the premium will be deducted yet again from your stores.

** Deep Ones: They have a ranged attack, but no reaction fire ability. So it's perfectly safe to position your troops for an optimal shot or run up to them at whack them with melee weapons. They are totally harmless during your turn.

* BlobMonster: The Calcinites, although they were contained in a humanoid diving suit.

* CloningBlues: Just about all of the aliens (except the Gill Men) are cloned, much like the first game. They don't have the personal autonomy to worry about it, though.

* InsaneTrollLogic: How your troops can survive taking hits that puncture their diving suits, and how they can use med-kits to treat injuries while underwater, is anyone's guess.

* EenieMeenieMinyMoai: They often show up on island Terror Missions, regardless of where in the world the island is actually located. Must be some kind of fad in 2040.

** The Triscenes are Implacable ''[[EverythingsBetterWithDinosaurs Dinosaurs]]'', until you find their weakness (their non-existent under armour).

* EverythingsBetterWithDinosaurs: They're heavily armored cyborg dinosaurs with Mounted Sonic Cannons.

* HumanPopsicle: The aliens use cryogenic stasis chambers to remain dormant for thousands of years. You can also sell these chambers as VendorTrash.

* ArtificialStupidity: Are any of the aliens in a given mission equipped with Sonic Pulsers? They'll also be carrying either a Vibro Blade, Thermic Lance, or Heavy Thermic Lance -- and yet they never use them, even if they've run out of Sonic Pulsers[[note]]This is due to a bug: the aliens can't functionally switch weapons, and their AI routines don't include melee attacks unless they have a built-in melee function (Lobster Men and Calcinites, for example)[[/note]]. You'd think this would give the player an advantage, but actually it makes these the game even more challenging, since instead of trying to make a suicide run against you to get into melee range, they will just spam you with grenades (a typical alien soldier with a melee weapon will usually have at least four grenades on them), which makes them far more deadly than a typical alien armed with a single-shot blaster.

* ArtificialStupidity: Are any of the aliens in a given mission equipped with Sonic Pulsers? They'll also be carrying either a Vibro Blade, Thermic Lance, or Heavy Thermic Lance -- and yet they never use them, even if they've run out of Sonic Pulsers[[note]]This is due to a bug: the aliens can't functionally switch weapons, and their AI routines don't include melee attacks unless they have a built-in melee function (Lobster Men and Calcinites, for example)[[/note]].

** Additionally, there are nonsense impediments to some of the important research tree, which lead to more bugs, which aren't game-ending but still make no sense. You need a live Deep One to research Ion Armor (the equivalent of the Power Suit from the original game), so if you roll unlucky and aren't aggressive enough, you may not see ion armor (and subs) until very late in the game since Gillmen quit running terror missions after a couple months.

* ArtisticLicensePhysics: Since TFTD is basically just a reskinned mod of the first game, a lot of the issues associated with underwater travel and combat are simply ignored. Ships are capable of traveling at supersonic speeds underwater which, even if you had a ship capable of surviving the feat, would generate massive amounts of turbulance. Your soldiers are able to throw grenades dozens of yards ''underwater.'' Furthermore, while powered armor can be used to handwave underwater mobility, your soldiers start the game wearing simple diving suits, yet have no trouble moving around under the crushing weight of hundreds of feet of ocean.

CreepyOldFashionedDivingSuit: The Calcinites are old-timey diving suits inhabited by strange, green blobs armed with metal claws. Ironically, they're only found in land-based Terror Missions.

* SequelDifficultySpike: Several aspects of this game make it harder than the first:
** Getting the most advanced armor requires capturing a live Deep One. While this seems simple enough, the problem is Deep Ones are only available on certain mission types, in which involve certain enemies (Gill Men). This means having to rely very heavily on RNG to get a chance to capture one. While Gill Men commonly show up in the early missions, they become less common as the game goes on, meaning if you miss the chance to capture one early the game, you could be stuck waiting dozens of hours for a chance to nab one later, all the while being forced to take on the game's toughest enemies with nothing beyond Plastic Aqua Armor. Trying to capture one early in the game has its own problems, due to your soldiers lack of experience and the lack of technology to make capturing enemies easier.
** Alien bases are now far larger, and have far more enemies then the first game.
** Rank-and-File enemies are now commonly armed with Disruptor Pulse Launchers, which can easily wipe out your whole team in one shot. In the previous game, only the highest ranking aliens had weapons this powerful.
** In the first game, aliens would only use grenades if your team members were grouped close together. In this game, aliens armed with melee weapons will routinely throw grenades at you whenever they are outside of melee range, even if your team is spread out.
** This game has no equivalent to the first game's laser weapons. All weapons in TFD require ammo, which makes managing the item limit for missions far more logistically challenging.
** The first game's Chryssalid was one of the deadliest enemies you could face, due to its ability to zombify your troops and civilians with a single hit. This game's version, the Tentaculat, is even more deadly because it can fly, which gives it the ability to attack airborne troops and ambush your team by going over walls. The only saving grace is that the Tentaculat is only encountered underwater, so you don't have to worry about it turning civilians against you on terror missions.

* UnwinnableByMistake: The game was initially released with some brutal bugs in the research tree that could ruin a player's chances of finishing the game without them even realizing it. Thankfully, patches and mods have fixed some of these problems:

* GuideDangIt: A Deep One corpse is also required to get aqua plastic armor, which isn't hard to get, but may not be an obvious leap if you are new to the game and leaves your men naked for longer. Even worse, to research the more advanced armors and watercraft, you need to capture a Deep One ''alive.''

* NoWaterproofingInTheFuture: Weapons and other technology developed (or reverse-engineered) during the decades of fighting in ''UFO Defense'' are completely useless underwater, so, in ''Terror from the Deep'', you must restart the researches from scratch. Consider it a {{Justified|Trope}} BagOfSpilling... that is, unless you're a clever enough hacker to exploit the similarities of the ''UFO Defense'' and ''[=TFTD=]'' engines and [[OldSaveBonus carry over goodies whose quantities were stored in the same data addresses]]. Partially justified by the fact that the alien gear needs Elerium, and the rest of the stuff is lasers. Still doesn't explain why they don't keep a few crates of lasers around for land missions, though.

''UFO'' cares about you. It wants you to have a good time. There is a bit of [[TheComputerIsACheatingBastard cheating]] involved (reaction time preference), but overall, it treats you nicely if you follow the house rules. ''Terror from the Deep'' is another ball of wax. That reaction shot will ''[[PerfectPlayAI always]]'' hit you, and you won't get a chance of surviving. Chrysalids can fly now. Particle weapons (Laser equivalents) have [[{{Nerf}} ammo requirements.]] Aliens holding one-handed Blaster Launchers. Certain weapons will function underwater [[PhlebotinumBreakdown but not on land.]] ''Multi-part'' Terror Missions. Only a Lobster Man Commander can get you the game-ending research, rather than an easier Aquatoid or Gillman. ''Terror from the Deep'' will put hair on your chest. It is a one-sided alien mosh pit of death and gloom.

* ObviousBeta: