Single player draft for a massively multiplayer game

I'm going to draft out the core combat for the browser mmo I want to make, in a single player gamemaker game. Because that way I know I can code it and see a working (single) player version, instead of trying to get one working in what I know of browser code (which isn't even the right word for it) and all the pitfalls and dead ends that'll involve.

One element I'm going to have is injecting a real sense and even possibility of instant defeat as the monster will have it's fighting approach described under it's name. You also have two attack options - regular and evasive. Normally evasive gives you a large penalty to hit. BUT on certain monster attack descriptions, the monster has a damage output potential that's going to have around a 75% chance of defeating a full health character (let alone a wounded one). If you hit evasion attack at these times, you still have the penalty to attack but you avoid the big damage attack entirely (no dice roll!)! You just have to keep watch while battling instead of clicking attack over and over and over.

Also I kept writing 'killed' instead of 'defeated' when drafting this. I'm not sure if I want perma death or not. I'll write about that gaming hot topic shortly!