Well, we also need to know what your objective is. Why do you introduce an experience curve? To decrease leveling speed? To force the player into leveling at different spots? What else?

xx + ?x + 20 = z
x = current level

At this point, you could probably plug any value into ? and figure out what you like. Say, for instance, you just want to make ? = 2.

1(1) + (2)1 + 20 = 23
2(2) + (2)(2) + 20 = 28
3(3) + (2)(3) + 20 = 37

If you want, you could make an Excel spreadsheet that will do pretty much all the math for you. I just can't remember the formula you'd use. >_>;;

Anyways, the other formulas, I need more clarity.

m = monster level
y = your level

For the monster formula, is it supposed to read like

[(m^2 + y)m]/5

or

(m^2 + ym)/5

Going by the order of operations, m^2 + (ym/5). Also, the flaw with you formula, either way you cut it, is that you're giving more experience to the player for killing the same monster as he levels up.

For instance, if you're a level 5 whatever and you kill a level 5 monster, you're going to to get 10 experience. If you're a level 10 whatever and you kill a level five monster, you're going to 25 (going by the second formula above). That don't make sense; you don't want to award a player more points for doing something that's easy than you would when it was hard.

I would recommend giving monsters set experience rates, which then could be distributed among each character or awarded to each character individually. Bosses also usually have set amounts of experience. If you don't go with the set route, I would remove the "y" factor from that equation, unless you'd want to go with something along the lines of:

m^3/y

That way, if you're a level 5 whatever and you kill a level 5 monster, you get 25 experience. If you're a level 10 whatever and you kill a level 5 monster, you get 7.5.

I've been working on these a lot recently, too, so I know how frustrating this shit is.

The monster experience formula should really take the form of:

monster level * (some value) / (some value) * player level ^ (some exponent)

If the monster is a higher level than you, you get more experience. If the monster is lower, you get less experience. The (some value) represents a modifier used to scale the actual experience numbers to whatever values you're using.

You might want to try fiddling around with a parabolic experience curve. The reasoning behind this?

A good story pulls the reader in with interest in the beginning. The middle gets complicated and builds stress, the end is catharsis and release. In terms of martial arts mastery:

For a beginner, a kick is just a kick. He's bad at the kick.

For the intermediate, a kick is complex and must be consciously managed for form, accuracy, etc.

For the expert, a kick is just a kick. But now he's good at it.

If your experience curve took the form of (some value) - (max level + player level)^2 = exp per level, with x being the player level, you'd have the right sort of curve. Essentially, it's easy to start with, harder towards the middle after the player has been sucked in but not hard to the point of frustration, and then eases up towards the end to relieve any stress.

Much better than just the exponential curve - no "fun" activity simply gets harder and harder as you do it. It gets harder to a point, after which you have a bit of fun before the activity is "completed."

Easy in the start, harder in the middle, easy again at the end. Game play difficulty, of course, is going to be increasing the entire time. Reward, however, follows a more natural schema.