Working on a Homebrew system loosely based off Iron Kingdom's d6 system. I'm going with a no classes, no level approach where you spend xp to buy talents and upgrade ability scores. How should I calculate xp costs? Looking for suggestions.

Don't know how XP is calculated, but it seems like the default is level based. So logically speaking, XP cost for all of a standard level's benefits should be the difference between the current level and the previous level, e.g. if it costs 10k to get to a particular level and 6k to be at the previous level, that level's benefits are worth 4k. You can weight individual benefits as a smaller portion with gradients based on importants, like this hit point dice costs more than that hit point dice, skills cost so many based on what their new value is after the level up, abilities that are level based cost this fraction of that level's difference, and so on.

If you want a skill-tree system, you need to consider the particular ways you want players to affect the game world. No system can be everything to everyone, and the ones that try either suck horribly or become hyper-modular nightmares of bookkeeping. Especially when they have point-buy going on or any kind.

Is the system supposed to be good for tactical combat? Then you want to make sure that equivalent effect on the battlefield is priced equally. Is it a social drama thing? Use the size of the social group an xp investment lets you influence as your metric. Kingdom building? Look at well-received board games for what kind of actions are given equal weight to which others.

Around this step, you want to consider whether you want to make it easier to specialize, suggesting narrower character concepts and requiring more attention to party cohesion mechanics elsewhere, or to generalize, which means you'll want to flatten some of the challenge range. Specialist systems have bigger jumps in both power and price at higher tiers of the tree that are bigger in power than price, making it most effective to specialize. Generalist systems are flatter on the players' end as well as the challenges, and you usually want the big xp investments to get you unique and flavorful capabilities, not (just)  big numbers.

Then, are there any specific player/character activities you think should be particularly un/common in your setting/thematics/genre? Tweak those to make them just slightly less/more xp-efficient so the mechanics actually support your narrative elements.
This message was last edited by the user at 23:18, Tue 14 Nov 2017.

Thanks for the input.