Killing your first Legendary, ever or in a single run, is a great feeling.
Doubly so if you did it without excessive usage of cover, head-on.
Killing an Enraged Legendary or a Nemesis monster before you even do a Legendary.
Finally figuring out the weakness of a particular enemy in LSD.
Bonus points if it's something very specific and you've been at it for hours.
Finally defeating the strongest monster of the current derivative you're playing, or its Final Boss.
CF's special Nemesis Macrocosm level is a CMOA for the entire mod and its development, ascending from a simple randomizer to having an actual ending.
Upgrading your plasma weaponry in CF, effectively making a lot of weapons you wouldn't use anymore relevant again.
Similarly, acquiring an upgrade for a basic weapon in LSD, which will turn them into a fearsome and destructive weapon compared to how they were before.
Pretty much every Complex Doom Invasion match turns into this after some waves, with tons and tons of monsters at once.
Playing Complex Doom Invasion alone with no teammates. The first waves are the hardest, then you're geared up enough that you can take the hordes on yourself.
The enemy designs themselves, if often basic to an extent, are also this.
The Cardinal in the original mod. Half a Cyberdemon levitating and able to use powerful magical attacks.
All the flying variants of the Spider Mastermind. Thought she was bad enough grounded? Oh boy...
The Legendary Zombie. There's a fair possibility that it will be the first Legendary you encounter, and its sprite is badass. He will be quick to overwhelm you with his Legendary Plasmatic Rifle if you're not careful.
The Legendary Revenant. Everyone's favorite animated skeleton, now stronger and creepier. It's easy to recognize him, because he goes Laughing Mad as soon as he sees you...
Not only is it basically impossible to kill, but it also has a second form, the True Legendary Cardinal, who is even more impossible to beat.
With the tools given to the player in Invasion, LSD and CF it is now fully possible to actually defeat this monstrocity, even solo.
The first battle aganist the Legendary Cardinal in Invasion's Tower of Sin map is everything good about LCA: an abundance of respawning player resources, epic powerup usage potential, and the encounter itself featuring the Legendary Sentient and the ability for the Legendary Cardinal to summon forth other Legendaries, all in a very nice, wide open arena map with space for all strategies.
The Legendary Cyberdemon, although not as mighty, also deserves a mention, as he was mostly Unintentionally Unwinnable himself.
Just when you think you've beaten him, Legendary Archviles teleport in and start reviving the Legendary Cyberdemon, turning the current map in a badass sequence where it is gradually resurrected into the True Legendary Cyberdemon.
The various demon runes. Ever wanted to be the Legendary Revenant? Now you may. Most of them include ALL of the demon's moveset.
The weapons naturally deserve coverage of their own.
The Legendary weapons, of course. Incredibly powerful weapons only restricted by a Like Cannot Cut Like rule.
The Legendary Assault Shotgun, an automatic shotgun with power far above the BFG 10k.
The Legendary Plasmatic Cannon. A ridiculously powerful, almost BFG-like gun that gets a nicer sprite in CF.
Naturally, everyone's favorite: The Legendary Plasmatic Rifle, the Demon Tech Rifle... but LEGENDARY! Incredibly fast, incredibly powerful, and a weapon of choice for many situations.
The Legendary BFG. An utter beast of a weapon, able to instantly kill most of the enemy roster, with a fancy, overdetailed sprite.
And you can upgrade it into the True Legendary BFG, allowing it to damage Legendary enemies.
The few lucky ones who have effectively defeated Legendary Doomguy in LSD will be treated with the prize of none other than the REAL TRUE LEGENDARY BFG, a separate, even stronger weapon.
The Demon Tech weapons are very cool themselves.
The Demon Tech Rifle, although a pretty common gun in Doom mods, never gets old. In LCA, it was the weapon with the best ease of finding/usefulness ratio, as a common zombie could drop it and it was first line aganist Legendaries.
The Demon Tech BFG 10k, based on the one of Quake 2 as opposed to the one in Skulltag (which in turn was loosely base on Quake 3's).
The Demon Tech Devastator, the ultimate gun in the original Complex Doom. Like the BFG... but cooler!
Complex Doom Invasion adds a fair amount of new Demon Tech weapons, including a Demon Tech Pistol, Rocket Launcher, and Repeater. The last one specifically has a very, very metal sprite featuring part of the famous crucified Jesus texture in Quake.
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