I've been looking through the potion code, but I could only find their ID's and how healing and about 2 other potions work.

All the potions are REALLY obfuscated on how they worked last I checked, from what I know fire resist works by the game checking if it's applied each tick before doing fire related damage, I managed to replicate this to make an armor set intercept specifically flame damage instead of both flame and lava. I know there is some kind of override or canceling function built for almost every type of damage, but I forget where I saw them...  As for strength, I don't really know too much about it, I would assume it would work somewhere in the player related classes and change your hit damage depending on whether or not it was active and what level it was, but other then that all the potions are extremely weird in how they actually function. What exactly do you want to do with these, I might be able to help you do it without using them

I was just trying to looking in on how to make the player fire proof, or give the player damage buffs without using potion effects.

 

I've tried using the extinguish method on a tick. Doesn't stop lava damage though. :I

Why not use buffs? There's not much bad about them, and you can just have them reapply each tick according to an if then statment...

I'm currently trying to make my own buff system, kind of like Terraria's.

Interesting, though it does make this quite a bit more complex, you could just use vanilla buffs but also show them on your buff screen/ tiles or wherever you want them, which could let the player cancel and see mini-images of all the vanilla buffs too. Other then that though, the actual way the buffs work is quite mysterious, I spent hours hunting down speed with no success.  :'(  I bet Lex or Hydro would know, but they might be too busy updating to 1.7...

Aww. 

 

Well, I guess I'll be sticking with Minecraft's buffs then.

 

Thanks anyways.

Strength potions (doing more damage) is handled by the Shared Monster Attributes system (SMAS).

 

Interestingly, while "I am not knocked back as much" effect is handled by the SMAS, the "I punch people and they go flying" effect is not.