Hello and thanks for taking the time to help me out. I'm running a campaign where leveling is milestone and story progression based but I am still having players keep track of their kills and achievements for experience point gain. I want to have the players use their experience points to purchase certain meta-gaming and in game effects, such as buying one time proficiency bonuses, re-rolls, auto-succeed, maybe even a GP/XP point exchange like 100 XP=1 gp. 

I was wondering if any other DM's have used this technique and possibly a menu if you will of things players could purchase. Thanks for the help and information in advance. 

I personally don't really care for the idea of being able to exchange XP for GP or vice verse, but a lot of these other ones sound like they could be good. Rerolling and auto-succeeding feel like they might be too strong, but one time proficiency bonuses are cool. Something to keep in mind is that the players will become very strong pretty fast with this, as they'll functionally be leveling up twice (the normal milestone level up along with what they buy in the experience store). There also wouldn't necessarily be anything stopping them from stockpiling these extra resources to steamroll fights, so perhaps putting a cap on how many they can hold would be a good way to prevent abuse (such as you can only have 2 re-rolls saved).

You could have feats be only acquirable through trading in experience. It should cost a pretty hefty amount, so that players can't just buy a bunch every session, but being able to customize your character with extra feats is always nice. You could also encourage roleplaying this way by placing certain conditions to unlock feats for purchase.

Thanks Glyth. I can see how overpowering the players is a risk, but I feel that if I make the cost high enough they will not be able to stockpile. I'm talking things priced in the thousands. As far as GP for XP goes I was thinking of doing something in the line of 1000XP could gain you 1gp or maybe 5gp. Again high cost for little return. 

Again thanks and if you find any menu examples I would appreciate the assist. 

I'd look at skill checks, saves, maybe even death saves, initiative rolls, inspiration dice. I'd look at a combination of +1, +2, advantage and D4 Inspiration dice (lasts until long rest).

I wouldn't make it tradeable for physical items like gold.

500-750 exp for permanent +1 HP

500 exp for a re-roll

1000 exp for a success - not a crit, just a pass. If there is no roll because the task is impossible, it cannot be bought.

What about letting them buy new proficiencies with the XP?

This sounds like an interesting concept, but I would set clear rules so there isn't any confuson and people trying to abuse the system. Maybe they could expend xp to gain a temporary magic weapon to help in a challenging battle thaat would save them from a party wipe lol.

Quote from Wysperra >>

500-750 exp for permanent +1 HP

Something to keep in mind with this system is that experience scales up dramatically as players level - for instance, sure, at level 4, 500 experience is a lot... but by the time you hit level 10, 500 experience is a drop in the bucket. With the quoted values, they go from +5 max hp bonus at level 4 (good, but definitely not broken), to +128 max hp bonus at level 10 (more than doubling their HP, broken).

You'll need to implement some sort of scaling system on the purchases. Could be something simple, like instead of 500 exp for +1 max health, it could be 100 exp for +1 max health, then 200 exp for the next +1, then 300, then 400... etc. Multiplicative might be better (50, 100, 200, 400, 800), but hard to say.

If you do additive (200, 300, 400, 500), it'd be +6 max health at level 4, and +37 at level 10, not nearly as over the top. This also means they'll branch out on purchases with their experience, as well.

Sounds like an interesting system.  I would vote towards just allowing them to spend the XP to buy Advantage on a roll, though I'd have it so that they have to declare this before rolling any die, not allow them to re-roll after they've already thrown their d20.  Something for them to spend when they really want to succeed on a particular task/attack.

As for how much it should cost, if it's not too much work I would say scale it.  Have it always be 1/4 of the XP cost needed to reach the next level or something like that.

Wow, I just looked back at this thread and I wanted to thank everyone who responded! Such great suggestions. Thank you all again. 

Xp was used as currency in previous editions, usually for making magic items. it wasn’t so great, that’s why they stopped.

In this case, if I’m a player, why would I spend xp to, for example, buy a hp, when that means it takes longer before I level, and when I level, I get a die+con of hit points, plus whatever other goodies I get from that level. 
And if you have some players use it more than others, you could, in theory, end up with a large gap in character levels, which makes combats really challenging to balance. (Yes the lower level characters, who spent xp for hp will be tougher than expected, but they’ll still have lower level spells fewer asi and, possibly, a lower proficiency bonus). 
This is a pretty fundamental change to the underlying game mechanics, and could easily end up with over- or under-powered characters. 

I kind of like this idea, but I think I'd take a cue from Zelda: Link Between Worlds with their item rental system. I think it would be interesting to have a shop or character where characters can purchase temporary boosts with a relatively small amount of XP, but if they want to keep them permanently it costs many, many times more.

I’d make a canon explanation for spending XP. Maybe there could be some cursed being (Like that cursed statue in BOTW, or a fiend in disguise) who trades XP for wealth (Gold or magic items or magic) as well as levels for wealth. Make this being creepy in some form of way so players would know that this being may have to do with the story, or maybe have dealing with that being too much result in negative consequences, which is good so even if the system you make is broken (which it may actually sound like great deals at the start) eventually show the true costs of what is going on, so spending XP too much may end up bad but a little bit is good which allows you as a DM to not have too overhaul too much of the game to do this due to players only bargaining in moderation. Maybe what the wealth given by the being is a boon, a strange but useful power, or an item.

I am not a fan of spending things for meta advantages because in my opinion it’s too videogame like and encourages some negative play styles like powergaming further. (Yes video games are awesome but certain videogame like mechanics can pose problems in D&D.)

Quote from Astalda >>

What about letting them buy new proficiencies with the XP?

 The character would also have to train to obtain that proficiency for the sake of realism however. It’s a little weird when some one is playing a barbarian and then out of random you are proficient at preformance.

Quote from _Nano >>

Quote from Astalda >>

What about letting them buy new proficiencies with the XP?

 The character would also have to train to obtain that proficiency for the sake of realism however. It’s a little weird when some one is playing a barbarian and then out of random you are proficient at preformance.

 Not the best example imo-I’d say performance is very much a skill barbarians learn as they advance. All their rites / rituals depend on performing In front of their tribes.

you could argue pretty much any skill is learned as you advance-you know,like  how wizards all of sudden figure out two new spells the instant they level....it’s just a trigger for the idea that they were learning it the entire time

Quote from Beowulfe >>

Quote from Wysperra >>

500-750 exp for permanent +1 HP

 

Something to keep in mind with this system is that experience scales up dramatically as players level - for instance, sure, at level 4, 500 experience is a lot... but by the time you hit level 10, 500 experience is a drop in the bucket. With the quoted values, they go from +5 max hp bonus at level 4 (good, but definitely not broken), to +128 max hp bonus at level 10 (more than doubling their HP, broken).

You'll need to implement some sort of scaling system on the purchases. Could be something simple, like instead of 500 exp for +1 max health, it could be 100 exp for +1 max health, then 200 exp for the next +1, then 300, then 400... etc. Multiplicative might be better (50, 100, 200, 400, 800), but hard to say.

If you do additive (200, 300, 400, 500), it'd be +6 max health at level 4, and +37 at level 10, not nearly as over the top. This also means they'll branch out on purchases with their experience, as well.

 The part you're missing is that they are spending the exp on HP (or other reward) instead of leveling.

As a sidenote, back in the back days, PCs would earn 1 xp for every 1 gp they looted from the bad guys.

Quote from HeathSmith >>

Quote from _Nano >>

Quote from Astalda >>

What about letting them buy new proficiencies with the XP?

 The character would also have to train to obtain that proficiency for the sake of realism however. It’s a little weird when some one is playing a barbarian and then out of random you are proficient at preformance.

 Not the best example imo-I’d say performance is very much a skill barbarians learn as they advance. All their rites / rituals depend on performing In front of their tribes.

you could argue pretty much any skill is learned as you advance-you know,like  how wizards all of sudden figure out two new spells the instant they level....it’s just a trigger for the idea that they were learning it the entire time

 

 

 Yeah true it wasn’t a great counter argument. But some skills are way more important to some characters than others and it may just be out of character to invest in certain skills. That’s my problem with XP to proficiencies. The potential for people to abuse it.