* AuthorsSavingThrow: The developers explained that the reason why Crimson Heads were not included in ''Resident Evil Zero'', after being retroactively introduced in the ''[[VideoGame/ResidentEvil1 REmake]]'', is because Rebecca and Billy don't spend as much around the same place as Alpha Team does in the ''[=REmake=]''.
* CompleteMonster: [[EvilutionaryBiologist Dr. James Marcus]] was one of three co-founders of Umbrella Corporation and a MadScientist without regard for anyone or anything unlucky enough to get in his way. In the late 1960s, Umbrella CEO Ozwell Spencer assigned Marcus to head the company's recently-constructed research center in the Arklay Mountains, which would also be used as a management training facility. Marcus seized the opportunity to use several of the trainees as test subjects for the newly-created [[SyntheticPlague T-Virus]], which he himself had developed in his lab by mixing the Progenitor Virus with leech DNA. At least 20 people were unwittingly subjected to his experiments, all of whom died and were either sent off to other laboratories for further research or dumped into the nearby sewers. In 1988, Spencer had Marcus assassinated following a decade-long schism between them; however, he was resurrected ten years later when his memories and consciousness were absorbed by his most recent creation, the Queen Leech, which had the ability to control other T-Virus leeches. Through the Queen Leech, Marcus set out to exact revenge on Umbrella. To do so, he leaked the T-Virus under the Spencer Mansion and on the Ecliptic Express, killing dozens of people and partly precipitating the crisis that led to the contamination of Raccoon City itself. He had every intention of causing large-scale destruction-- when Rebecca and Billy finally encounter him, he gleefully expresses his desire to destroy the entire world. Callous and amoral, Dr. Marcus's complete lack of humanity predates his transmutation into a ''literal'' monster, which merely gave him the means to demonstrate the true and terrifying extent of his depravity.
* DemonicSpiders:
** The leech zombies, without a shadow of a doubt. Tough as nails with an insanely long reach, they cause considerable damage when they hit, and when they die, they ''explode'' for even more damage. Luckily, [[KillItWithFire fire kills them]] fairly quickly, mitigating the annoyance a bit.
** Eliminators are small, soak up more damage than they have a right to, attack in packs, and like dodging bullets.
* EnsembleDarkhorse:
** Despite being the game's focal character, Rebecca still counts as one as for the series as a whole. So her fanbase was pleased to see her get her own game and they hope to see more of her in the future.
** Billy became fairly popular. So much so that his fans desperately want Creator/{{Capcom}} to reveal [[spoiler:whether he survived the Raccoon City incident]].
* EvilIsSexy: The young James Marcus seems to have been invented for the sole purpose of adding more {{bishonen}} to the series.
* FanonDiscontinuity: Fans who don't like ''[[VideoGame/ResidentEvilGunSurvivor Resident Evil: Survivor]]'' have been known to use the ContinuityNod to declare ''Resident Evil Zero'' non-canon.
* FanPreferredCouple: Many of the game's fans have admitted to have shipped both Billy and Rebecca. Even the collab review done by WebVideo/{{Caddicarus}} and WebVideo/JordanUnderneath have them indirectly shipping these two.
* GoddamnedBats: Actual bats, too!
* HilariousInHindsight: The submachine gun that's unlocked after beating the game with either an S or A rank on Normal or Hard mode strikingly resembles the SIG-Sauer MPX, which was released approximately 13 years after the game.
* InferredHolocaust: One [[WildMassGuessing possible reason]] [[spoiler:Billy]] didn't show up in later games? The last you see of him is him walking into a forest infested with man-eating monsters, unarmed.
* {{Narm}}: It's ''Resident Evil''. [[Narm/ResidentEvil What did you expect?]] Special mention goes to [[spoiler:Dr. Marcus]] controlling his leech doppelgängers through a countertenor opera solo.
* ScrappyMechanic:
** Unlike previous games, there are no crates for you to store your stuff in. Instead, the inventory system here works by having Billy and Rebecca ferry stuff you need from one area to the other.
** Rebecca is disgustingly frail. While this may have been intentional to put more emphasis on Billy being the fighter of the two, there's a difference between can't take much punishment and "three Eliminator attacks send Rebecca into orange caution status". It's frustrating using double the healing items necessary if you're not careful; but the game also has aforementioned Eliminators and leech zombies who are hard to avoid regardless.
* VindicatedByHistory: ''Resident Evil Zero'' had to compete with being released after the ''[=REmake=]'', which considering the incredible reception to that game, was no easy task. It also introduced a lot of new features like the partner system and lack of item boxes, and both were disliked by just about everyone. With the HD re-release of the game, however, a lot of detractors to the game have been much kinder to it, and have stopped comparing it to ''[=REmake=]''. It's now regarded as a flawed, but ultimately entertaining and unique entry in the series.
----