This mod adds a new enemy: the assassin. These enemies will start off in stealth with slow movement. If they are attacked or attack the player, they get out of stealth. They deal bonus damage from their attack while in stealth, based on which biome they are in (wasteland hits the hardest, forest the weakest). If the assassin cannot attack the player for a few seconds (about 20), they will return to stealth, reducing their movement speed again.
This is a modlet and does not require a world restart. Simply place into Mods folder and play!
Tested and works with Alpha 19.2 b3
Recommended to be played single player or multiplayer. Works fine on servers as well.
The forum topic of the mod is here.