V20 and V5
What's the Deal?
The 20th anniversary edition, technically the 4th edition of Vampire, was released in 2010. It was written as a way to update and smooth-out the sheer amount of content that had been produced in the 20 years. In an attempt to draw more players back to the system, and entice those from more popular games (such as D&D), 5th edition was released in 2018 as a complete overhaul of the mechanics, lore, and metaplot. In other words: editions before V5 should be treated as another system entirely, because of how vast the modifications were.
Mechanical Differences
Dice Systems
One of the main differences between the two systems are how dice rolls are handled.

V5 has custom dice with symbols denoting what type of result the roll was, with your dice split into two parts depending on your current Hunger. The difficulty of the roll was how many successes you needed to achieve the desired result. But, results could vary from messy criticals to bestial failures depending on what values came up.

V20 instead relies on standard d10s. The difficulty of a roll in V20 is the number the die has to equal or above to count as a success, with the degree of success (how many successes you gained) determining the achieved outcome. Any 1s rolled will subtract from the total number of successes. If you roll any 1s and have no successes, the result is a botch: an action that went horribly wrong somehow.

Unlike V5, your blood pool has no effect on your normal dice pools (attribute + ability combinations).

Important

We use the botch rules from revised. This means that any number of negative successes will count as a botch, not just if no successes are rolled.

Willpower
While willpower allows you to reroll dice, in V20 spending a point gives you an automatic success on the roll regardless of the outcome, but must be spent before the roll is made. This can turn potentially scene-altering botches into a bare-minimum success. As written the only two rolls that you can't spent willpower on are willpower itself and degeneration.
The Blood
Blood Pool vs Hunger

Instead of rouse checks, all characters have a blood pool which is comprised of blood points. Blood points can be spent on a variety of actions, such as blood buffing and blushing, which is all detailed on page 268 of the core rulebook. Because of this, hunger isn’t represented with actual dice, but as a threshold: 7 - Self Control. At this number of blood points and below, the character is considered hungry, which will incite rolls versus frenzy when in certain situations.

Important

You are able to have a full blood pool without having to kill someone unless special circumstances dictate otherwise. A few nights of successful hunts is normally enough to keep someone fed, especially with how populated LA is.

Blood Potency

Generation is the only ‘glass ceiling’ in V20. It only limits your trait dot maximum, how many blood points you can spend per turn, and the size of your blood pool, nothing else (such as the amount of damage you can heal, dice bonuses, and feeding penalties).

Blood Resonance

Blood, for the most part, is blood in V20. Unless required by a derangement (such as sanguinary animism), blood provides no mechanical emotional impressions. Old/Dead/Preserved blood and animal blood is disgusting but gets the job done. Anything fresh from a human being is euphoric, and Kindred vitae even more or so.

Predator Types

Another thing that isn’t represented mechanically in V20. If your character has a preferred way of hunting, that should be detailed narratively through roleplay, and the type of hunting rolls they use. There’s no mechanical ‘instinct’ forcing them to hunt a certain way.

Disciplines
V5 condensed and nerfed a lot of the disciplines from V20. Some of the bigger differences you should be aware of are:
  • Potence, Celerity, and Fortitude do not have individual powers, and are instead passively added to Strength, Dexterity, and Stamina (soak) respectively. Potence and Celerity can be used more drastically with blood points, whereas Fortitude is the only way aggravated damage can be soaked.
  • Many disciplines that were combined are completely separate in V20: Protean, Serpentis and Vicissitude, Dominate and Dementation, Obtenebration and Necromancy, and the various types of blood magic (such as Thaumaturgy and Dur-An-Ki).
  • Disciplines only have one ability per dot rating, and characters have access to any abilities of the dot rating they have and lower for any disciplines they possess.
  • Thin-blood Alchemy is a V5 exclusive mechanic and doesn’t exist in V20
Morality
V20 uses a much more rigid morality system than V5. Instead of setting tenants for your chronicle, all characters are on Humanity by default. Degeneration happens when a sin of equal or lesser value to a character's current rating is committed. This normally takes the form of a roll (Conscience difficulty 8), though particularly horrific actions can warrant a dot being taken outright.
Damage Types
There are three types of damage in V20: bashing, lethal, and aggravated.
  • Bashing is blunt force trauma, with the exception of firearms. All characters can soak bashing damage, though because a Kindred’s undead body doesn’t bruise easily, any bashing they receive is halved after soaking. A single level of bashing can be healed with 1 blood point.
  • Lethal is, as it’s name implies, damage with the intent of being lethal. While a punch would bruise, a sword can do considerably more harm. Lethal is the highest form of damage a mortal can receive, with medical attention required in order to heal. Kindred can attempt to soak lethal damage, but this value isn’t halved. A single level of lethal can be healed with 1 blood point.
  • Aggravated is the biggest threat to Kindred. It’s sources are always supernatural in nature: fire, sunlight, a lupine’s claws, etc. The only way Kindred can attempt to soak aggravated damage is through their fortitude dots only. Conversely, any damage that would be considered aggravated for Kindred is taken as lethal by mortals (with the exception of sunlight, as they remain unaffected). Healing aggravated damage is taxing, requiring 5 blood points and a full day of rest to heal a single level. More levels can be healed, though that would require spending an additional 5 blood points and 1 willpower per additional level healed.

Its important to remember that a full health track of bashing or lethal damage will only send a character into torpor, while a full track of aggravated will cause Final Death.

Willpower damage is a another mechanic exclusive to V5 with no representation in V20.

Social Combat
Social encounters are roleplayed accordingly, with social rolls made should they be necessary. Actively 'damaging' someone with a witty retort isn't possible in V20.
Merits and Flaws
Merits and Flaws have a point scale rather than one made of dots because they impact freebie points: points given at character creation to round out a sheet mechanically. Merits are bought with freebie points, and flaws can be taken to have more points, up to a maximum of 7 additional freebie points in flaws. Note that merits and flaws are entirely optional, but highly recommended.
Metaplot Differences
Because this is subjective to the chronicle being played, the information below is V5 in comparison to our (LAiA's) specific setting.

The goal was to advance our setting in a similar direction to V5, but in a different way. The important notes are as follows:

  • No events or characters from Vampire: the Masquerade — Bloodlines are considered canon
  • The Anarch Movement has become the most populated sect, following the Sabbat. Unlike V5 this was not out of choice by the Camarilla, who are scrambling to try and regain members.
  • The Sabbat is still in North America, with their idle radicalism further deteriorating their strongholds (notably Montreal, Mexico City, Detroit, and now Washington DC).
  • The Lasombra and Tzimzisce remain aligned with the Sabbat.
  • House Tremere was fractured, though their bonds to the pyramid weren’t broken. Instead, those who decided to join the Anarch-aligned House Carna participate in a ritual that bears suspicious resemblance to the vaulderie to break their old ties.
  • The Giovanni, Harbinger of Skulls, Samedi, and remaining Cappadocians continue to be separated rather than form the Hecata.
  • Thin-bloods (those of the 14th and 15th generations) are considered Caitiff rather than a different category
  • The Beckoning isn’t a thing; elders aren’t being forced anywhere