Beefy Kasplant

It's pretty much point by point: 
 
Create a global variable, call it: NPCKilled
Go to the NPC editor and add an event on NPC death: 
Add +1 to global variable NPCKilled
 
Create an event in the main town:
Page 1: Condition -> NPCKilled < 25000
Show text: You haven't killed enough NPC
 
Page 2: Condition -> NPCKilled => 25000
Show text: Hurray, you managed to decimate the NPC population beyond repair! Their species will never recover from this massacre!

Global variable
NPC kill event: +1 to global variable
 
Some event NPC or something that does something when global variable => 25000

Only with source edits

You can't change the animation based on the direction without source edits

Server config: 
 
Drop chance: 100%

1. Source code I assume
2. Global event on  NPC death: Chatbox message: \pn killed boss! (Not sure if it's \pn or some other command)

Yeah, it will fire a spell when it hits a target. 
 
So you could make for example a rocket launcher and have a projectile that fires an AoE explosion when it hits. 

yes

Make sure the url to the upload.json is public guys!

They won't work but there are some converters floating around with which you can probably convert your sprites in 4 frame variants.
 
And otherwise it's possible to just edit the source to make it work 

Yeah, without source edits you're going to have to make multiple equipment slots as mentioned above. 
 
You will probably run into some issues if you don't make a distinction between the different gem slots though. In case people want to equip their gems, but the gem they have is for slot 1 and not for slot 2. 
 
You can get around this by having a 'Soul Gem' type, 'Body Gem' type, etc.  

ShareX. Hands down the best

There's no skill tree editor that you missed lol.
 
I wish there was but unless you edit source, you'll have to mess around with shops and events 

In the server folder you can find the damage formulas and you can change them to work how you want 

edit your sprites to be 3 pixels lower or your paperdolls to be 3 pixels higher

Same size tile with more pixels? The tile size is in pixels, so what you want is impossible

In the server(?) config you can set the rendering order of all your paperdolls per direction. 

In the server config you have to add under Map

    "ZDimensionVisible": true,
 

No, anything that requires character animations, new windows or buttons and most visual stuff needs to be done through source edits

It's already in the class editor. 
 
Use the `stat points` box

Nope.
 
 

Yeah you can have an event that runs on level up. 
 
Just add a 'play sound' command

You can't 

Need to modify source massively

So you level up 36 times:
36x120 = 4320 
 
Base level is 50 hp
 
4370
 
 
Works fine bud!