Note: Babel Requires GZDoom 4.2.0 or above.

\\\ Design

Babel was designed around the concept: What can be added to Doom that makes the game more dynamic without detracting from the core gameplay experience? To that end the mod is pretty heavy on the gameplay tweaks and contains a few completely new systems that the enemies use, but overall shouldn't feel overly unlike Doom. An imp is still an imp, but in Babel the imp isn't just a meatbag with a weak attack, it's trying to kill you like a demon would. In addition, each weapon has been molded to fit a certain general role so that each weapon has its own applications and role that it's good at. There's still definitely a power scale in the arsenal, but no weapon ever gets completely obsoleted.

(Please Note: Babel is intended to be played on Erelim difficulty with quicksaves and continual progression, and on maps whose difficulty approximates the vanilla IWADs. Pistol starting, Ironman, or using maps with vastly higher difficulty will result in a much more difficult experience. Mathematically, these maps should be completable. Computationally, maps with thousands of active monsters may chug GZDoom. Realistically, your fleshy human brain may not be able to work fast enough to avoid death.)

\\\ Synchronization and Chaining

In addition to the plethora of new enemy attacks in Babel, the key enemy-benefitting feature that has been implemented is Sync-fire and Chain-fire. Simply put, synchronization is the ability to tell other enemies that you are attacking, and those enemies can choose to join the attack. Chaining is the ability to tell other enemies you have finished an attack, and have them continue it for you. Monsters generally have one of these abilities, never both, but sometimes they lack them entirely in special cases. What this means is that monster groups are often far more aggressive than in vanilla, and softening up a horde will have the secondary effect of reducing the amount of sync/chain signals being sent, reducing aggressiveness.

In more detail, a good example of synchronization is a group of imps. Whenever an imp begins an attack, it sends out a signal to all other imps that it can see (within a certain range). Each of those imps has a certain chance (which in this case is ~40%) to choose to join the attack, and if it does it then determines if it can actually hit with an attack. If it can, it then also initiates an attack. It's important to note that joining a synchronized attack does not send out another sync signal, so cascades do not occur.

An example case for chaining is the Mancubus. Like the imp, it can share attack information. Unlike the imp, mancubi send out signals at the end of their attacks instead of the beginning, and the chaining monsters can themselves send out chain signals. This means that one attack can "continue" through several monsters, creating a non-stop flood of attacks. However chains in practice differ from syncs in that syncs often begin with many monsters attacking and end with only a few, whereas chains begin with one monster and often end with many attacking.

Some monsters can chain or sync to monsters other than those in their species, but those are relatively special cases. Most of the time a monster will only signal monsters of the same type. Killing monsters sometimes sends out chain or sync signals, and some special monsters can also sync up non-attack abilities.

\\\ Fear

Now of course it wouldn't be fair to have these powerful new monster abilities without something for the player right? Fear is that thing. Most monsters are now no longer totally mindless and can be frightened with the appropriate amount of coercion. All monsters except zombies, lost souls, spectres, bosses, and the archvile now have internal fear meters. Things like killing their comrades, firing weapons, causing explosions, etc. will cause them to build up fear. Once they're scared enough, they may lose their will to fight and flee. Bear in mind that a group of monsters can retain its composure faster than a single scared individual, and the stronger a monster is, the harder it is to scare them away. However the stronger a monster is, the scarier it is to its comrades when you kill it.

Some monsters, notably the hell nobles, have attacks that can reduce fear in nearby enemies. This makes them prime targets when facing large groups, as inflicting fear is a powerful tool to survive aggressive play. Killing a boss will also scare nearly every monster which witnesses it, only by chance can they retain their ability to fight.

\\\ Weapon Roles

One of the things that bothered me about Doom 2 was that the weapons, while very fun, often had far too much crossover in its effective role. Notably, the chaingun obsoleted the pistol entirely and the super shotgun was almost objectively better than the shotgun, barring accuracy at long distances. In Babel I've tweaked the slot roles to conform to the following pattern:

 * Slot 1: Melee. Berserk now affects the chainsaw as well as fists and berserk punching leeches small amounts of life when under 80%. Melee in general now does more damage. The Chainsaw has special interactions with Demons and Spectres, stunning them much more readily than other weapons and largely preventing Spectres from using their teleport to escape.
 * Slot 2: Accurate but weaker weapon. Good for sniping or taking out smaller targets. 3 options here, with slight variations on the theme. The PSMG is the least accurate but recharges ammo. The Heavy Pistol is the most damaging and accurate, and also has a 50% higher chance to inflict pain per attack, but has recoil and cannot be continuously fired at full accuracy. The SMG has the highest fire rate and mid-level damage, and serves as a more accurate, less damaging chaingun.
 * Slot 3: Shotguns. High burst damage but lower fire rate. Notably, the shotgun is now exactly 1/2 of a SSG in power and accuracy. Shotguns can also be swapped at any time during their reload, but the reload must finish once they're re-selected. For the shotgun, this means the weapon must be pumped. For the SSG, shells must be replaced and the weapon must be closed, but the weapon will remember what stage of reloading it was in when it was swapped (shells never eject twice, etc).
 * Slot 4: Huge DPS and stunlocking weapon. The chaingun is now quite unsuitable for sniping, but in exchange can tear through both ammo and demons at lightning speed. Not much can even bring itself to attack through the hailstorm of bullets the chaingun now fires. The chaingun also does extremely consistent damage per shot, allowing smart users to conserve ammo by remembering kill timings.
 * Slot 5: AoE weapon effective at all ranges. The rocket launcher also received a 50% damage buff on its explosions, and is very good at inducing fear. Rockets also accelerate in flight slightly, aiding in long-distance shooting.
 * Slot 6: Huge DPS Midrange weapon. The pulse rifle, which replaces the plasma gun, is great for DPS but fires slower than the chaingun and as such is not as good at stunlocking. Pulse bolts are also faster when initially fired and slow down in flight until hitting ~25u/s, discouraging sniping in favor of the rocket launcher.
 * Slot 7: High Cost Screen Clear/Panic Button. The BFG's workings have been changed dramatically. It now attempts to kill every enemy onscreen in order of beefiness, but can easily be less efficient than the pulse rifle if not used in situations that demand it. As of the newest version, it can also be charged up to use more ammo but also inflict more damage at once, though it still cannot inflict more damage in one shot than it could when uncharged. Instead, if there is an enemy with more than 2400 health, it will be hit with 2400 damage and the extra damage will target other monsters in view.

\\\ Other features

Babel also has a few other QoL features:

 * Autosave, by default every 3 minutes. Can be turned off if desired.
 * Health pickup splitting, If you grab a medkit the game will attempt to conserve any leftover healing into stimpacks.
 * Ammo splitting, as with health, ammo will attempt to break down into smaller pickups so you don't waste any.
 * Smart armor pickup, you will not pick up new armor unless it actually gives you a potential durability benefit. Pressing "use" while aiming at the armor will override this behavior. No more accidentally grabbing green armor when you wanted to keep blue.
 * Immensely configurable visual options, nearly every extra visual effect can be toggled, for those who need more performance or prefer a "purer" experience.
 * Low health warning built in, can be disabled.
 * Monster sprite fixes from the Doom and Doom 2 Minor Sprite Fixing Project (link) integrated in mod by default.