This mod adds many new things as blocks, items, armor, biomes and 2 new dimensions. Main mob of the mod, after which the mod is named is The Professional Killer. This mob is fully green with sad, or I would say displeased face. It fights every living creature: animals, villagers and illagers, player. He doesn't fight other mobs. When he dies he drops his heart. He spawns in the Stone Beach biome or in new biome called The Dread Forest.

Now I will talk about other things. Also there is a mob called Guardian Slime. I didn't use slime model as for some reason, MCreator I can't import custom models and it gives me an error. So I painted the texture and that's why he vaguely, I repeat, vaguely resembles a slime. He spawns when you use new slime sword or from slime fruit which you can find in the Slime World. This mob won't attack you but defend you.

Also, you can craft Professional Killer's costume. This is only cosmetic armor, mobs won't think that you are The Professional Killer. If we returned to The Professional Killer, let's talk about his nightmare version. You should craft a new block called The Captured Evil. You craft it from Soul Sand, Killer's heart and Iron Bars. If we will activate it, we will summon his nightmare version. Now he is smiling, there's blood on him and he will attack everything he sees. After we defeat him, he will drop Heart Of Evil. If it's in your hand and you will hit mob you will hit him strongly! But sometimes it will absorb you: hurt you. Since it only hurts directly, we need to cover it with iron by combining it with it. We will get new type of metal. Unlike the Heart, it won't damage you. Combining it with new flower, Flower Of Kindness, which you can find in new Mushroom Forest biome, you will get the Sword Of Power. It uses power of evil, but this magic flower redirects it on Undead Mobs. If you use this sword on undead you will kill it! He will deal them 24 points of damage!

There other things but they're petty. New dimension, Monster Shelter (I said about Slime World then so I'm not saying about it now), world full of agressive mobs with new structure. One new biome, Redland (I said about Monster Shelter biome then so I'm not saying about it now, and I'm not saying about biomes other worlds are of), with red vegetation. New flower, Gray Flower (I said about Flower Of Kindness then so I'm not saying about it now). New Utility Tool: Killer Tool which kills the mob instantly. Compressed Slime, a block you can't craft, but you can find in Slime World. And I added new tag: Slime items. The only thing I haven't talked about yet is how to build portals. To get to Slime World build obsidian portal and light it with new igniter. To get to Monster Shelter world you need to build portal from New Rotten Obsidian block and light it with another new igniter.

Also this mod has a Wiki!

Link: https://the-professional-killer-mod.fandom.com/wiki/The_Professional_Killer_Mod_Wiki.