This Developer Blog is copied verbatim from the RuneScape website. It is copyrighted by Jagex.
It is written by Mod Maylea and is dated 28 October 2009.
Impetuous Impulses

My latest project is to rebalance and update a minigame I am quite fond of: Impetuous Impulses. It’s a fun piece of content for the drops it can offer (ah, the thrill of spotting the vivid orange of a dragon impling!), but sadly isn’t so rewarding XP-wise. So what’s the core of this update?

First we’d like to make the Hunter experience earned a bit more rewarding so that you have the satisfaction of gaining XP as well as the drops. Then we’d also like to give high-level hunters a few new implings to hunt. We have a few other things in store for this update, too, but what would be the fun if you knew everything in advance? :)

I’ll also keep a veil of mystery over the theme, level and drop tables of our latest impling additions for now, and instead will focus on the bigger challenge of this project: how do we go about rebalancing XP values in the game?

It’s a bit more complicated than picking a number at random and hoping it’ll work okay. There are many parameters to take into account to try to come up with the best value.

The existing XP rate

The first thing to do is to assess what we currently have. That involves evaluating, from the numbers in the code, how many of each impling spawns on average in Puro-Puro and on RuneScape's surface, and what the average value of their drops is.

Then we need to have a good idea of how much experience a player is getting already when playing the minigame, because even though we know how many of each impling there are, on average, in the maze at any one time, we do not know how easy they are to catch.

We do this via time trials. Basically, some members of the QA team will diligently play through the minigame for a certain amount of time, catching certain types of impling and making notes of how much XP and what drops they are getting. After a few attempts at each level, we calculate the average XP rate per level. This will be our base rate for the improvement.

The best XP rate

But we wouldn’t want the XP to be too generous. Yes, I suppose some of you would like it to be too generous, but think what would happen if it was: the once peaceful minigame would become a training area, and while I do appreciate the game for the drops (and the thrill of using one of the mysterious crop circles), I don’t think it would be anywhere near as fun if I had to catch as many implings as possible and throw away the drops for the sake of XP.

We can still make the XP fairly nice, though, but to know exactly what our limit is, we need to know how much XP a player can gain when training Hunter normally. With the help of some more time trials, we evaluate how much XP per minute can be gained when hunting other hunter creatures like salamanders or chinchompas. That is a lot of info to compute, so we use tables to sort it all out and represent it using pretty curves.

The final recipe

Xp rates

Hunter XP rates graph

Now that we know the existing impling XP rate and the best Hunter training rate drawn on our graph, we have the boundaries of our new curve! The rest is a bit like cooking. You determine a base curve that sits between the existing impling XP rate and best Hunter XP rate. You throw in a pinch of level requirement, one or two spoons of spawn repartition and maybe powder a bit of drop value on top. You mix, the curve wiggles a bit up and down as it gives more XP to rarer or less generous implings, then you season it until it looks good. Ta-da! You have one nice rebalance! The last step is to time trial that a bit too, to see if it tastes any better.

Hopefully, the result will be satisfying without upsetting the game's balance (else Guthix wouldn’t be best pleased).