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Enemy Variations X

Enemy Variations X is a mod that adds 'variations' to all existing NPCs.
This also means you can replay Half-Life with these variations applied.

You could run into an exploding headcrab, a hardly visible combine, an antlion that knocks you back, a manhack that spawns baby manhacks,.. etc

Some variations are more 'rare' than others, so you're not going to run into a big boss that deals 4x damage all the time.

Please report issues, make suggestions or give me feedback in the comments.

Knockback (purple) knocks you or props back, higher level increases their knockback effect
Puller (green) attacks stun you and pull you towards them depending on their weapon's damage force, higher level increases the pull and stun timer
Explosion (red) explodes upon death, higher level means larger explosions
Cloaked (white) hard to see, half health, deals more damage depending on their level
Mother (yellow) spawns 4 babies upon death that are 1/3 original health but have damage that depends on their mother's level
Boss (dark gray) 8x health, deals more damage depending on their level, up to 4x at Lv. 100
Bigboss (teal) 16x health, deals more damage depending on their level, up to 8x at Lv. 100
Rogue (blue) hates everyone except their own exact kind (for example, rogue headcrabs won't attack headcrabs, but they will attack zombies)
Lifesteal (blueish-green) their attacks have lifesteal, up to 4x lifesteal at Lv. 100
Pyro (orange) their attacks set you on fire, the duration of being on fire increases at higher levels
Metal (chrome material) only explosive attacks deal damage to them
Gnome (tealish-blue, tiny) their attacks set health to 1hp and taunts
Gas (green) Emits a cloud of gas upon death, the gas deals recoverable damage, the size of the gas cloud increases by level
Spidersack (dark green-brownish) Spawns tiny baby spiders upon death, more spiders at a higher level, the tiny baby spiders only deal 1 damage and will die after 1-5 minutes
Possessed (transparent black, unstable looking) Pulls all props around him towards his corpse upon death, the radius and strength of this increases at a higher level, also teleports around like a freak
Mix2 (shiny flat color in the two variation colors) A mix of any two other variations
Detonation (orange) Think Minecraft creeper.
Chimera If he spawns I hope you're ready.

Players can get a variation through enemy drops called "essence".

You can press the USE key on essence to eat them and gain their effects. The player will then gain the same effects as the variation does for the NPC. This way, your weapons can gain knockback, you can deploy gas, you can get damage increase, etc.. as a player. These player variations run on a timer that is lower the higher your essence's level is.

Variations that would normally only work when you die (like the 'explosion' variation) will also double as deployables for a player. In the case of the 'explosion' variation, you can then choose to either die (and explode like normal), or crouch and press secondary fire to 'deploy' an explosion at the aimed position. Currently only explosion, gas, possessed and mother are also deployable.

You can customize EV-X to your liking.
Open the menu when you're in a map and go to Utilities -> EV-X to do so. Here you can adjust spawnrates or set general settings.

If you're into that, all settings are available through console commands:
evx_enabled 0/1 - Enable or disable evx's influence over NPCs entirely
evx_affect_allies 0/1 - Whether allies like Alyx, rebels,.. can get variations too
evx_use_colors 0/1 - Whether variations should be visible as a color applied to the NPC
evx_rate_(type) - Set the spawn rate of any ev-x type, rates are relative to all other rates, so if you want something to be super common, just put 100000 (the maximum)
evx_rate_reset_all - Resets all spawnrates to their defaults
evx_randomize_on_rate_change 0/1 - Whether to re-randomize existing NPCs when you change spawnrates
evx_draw_hud 0/1 - Turns the hovering hud on/off
evx_random_spiders_chance 0-1 - 1 means 100% chance of random spider babies spawning on props, 0 means no chance at all
evx_allow_music - Enable/disable EV-X music events, like boss spawns
evx_essence_chance - Odds of getting an essence drop from an enemy, 1 means 100% of the time
evx_essence_timer_factor - Multiply all essence timers by this amount, 2 would make all essences last twice as long

You can right click an NPC to set a specific variant or level on them.
DO NOT MAKE SAVES like this by placing down specific variants, it WILL NOT save which variant is where, they will all be randomized again on map load.

This is not just my project, but ended up being a project of the community. (If I forgot anyone, kindly contact me!)
You can also view these credits by spawning the "Credits" EV-X entity ingame!

Mercury - gas idea
ts.5678 - player variations
Vladbzf - puller idea, pyro, lifesteal, stun/puller idea
Lord Crown Empire - pyro idea
Jerkakame - rogue, gnome, bulletproof, possessed, levels, level = color intensity idea
Darkjake - remove colors idea