Duplicates every enemy in the game, including bosses. Clones have their event IDs removed, so you will experience some fun things like bosses leaving their arenas and swarms of friendly NPC summons coming to help out.
Nearby enemies no longer prevent you from sitting at bonfires because some would be basically unusable otherwise. Any time you enter an area you'll get a smattering of souls from unfortunate clones falling off the map; enjoy it, because you'll need the help.

Most of the game is very hard but still doable on 3x Enemies, but some bosses are practically impossible on your own. Even on 2x you will have an extremely difficult time in a couple places. Please don't be shy about switching the difficulty if you get stuck.
You may also notice a vanilla mechanic that usually doesn't come into play very much: most enemies will calmly stay out of the way if you're already being attacked by a few others. If you find that a little underwhelming, the "Impolite Enemies" optional file will remove their qualms about ganging up on you.

WARNING

To the best of our knowledge the base mod is safe to use online, but if you don't plan on playing with a friend I recommend you switch to offline mode just to be safe. Other players who don't have the mod will just see you getting beat up by thin air anyways.

On the other hand, the Impolite Enemies addon WILL ABSOLUTELY GET YOU BANNED. DO NOT USE IT IN ONLINE MODE.

Installation

• Unpack DS3 with UXM.
• Pick one of the enemy number options and copy the map folder from it into your game install.
• If you want Impolite Enemies, copy Data0.bdt from that folder into your game install.
  

Onslaught is compatible with new or existing saves and can be installed, removed, or changed at any point.

Uninstallation

• Restore the vanilla files provided in the Vanilla folder.