We met David at PAX West 2017, and he told us about his great system for using the different types of D20 coin at the table. We asked him to write it up. He also includes some of the limited edition finishes we have made in the past. We hope it gives you your own ideas!
This is the Inspiration system I've been using for 5e.
I am absolutely terrible at handing out Inspiration during my games. I grew up on 2nd edition, so I just never got into the habit of it, and old non-habits die hard. The solution that I came up with was to give my players each a token, one of the silver-finish d20 Coins from Campaign Coins at the beginning of every session. They were allowed to use these tokens to grant only *another* player Inspiration, and could not use them on themselves. This worked very well, and was well received by my players, becoming another resource which the group managed at the table and allowing for them to show camaraderie very directly.
I had, though, begun collecting all of the various finishes of d20 tokens made by Campaign Coins, and it gave me an idea: what if players drew the tokens at random at the start of each session, and each different finish gave a different effect. They would all have to be fairly similar in use, though subtly varied, and I'd want each one to still feel useful to the person who had it, so there was no one left feeling they'd gotten a bad draw that week. Here's the effects I eventually settled on...
"This coin can be used to grant +1 to any roll. This effect may be used after a roll is made."
This one is the most difficult to use, probably. My players tended to be very good at deducing a target's AC after a few rounds of combat, and this ability would let them turn a narrow miss into a hit. Of course, if the players already know the DC of a roll, it's even easier. There's always cheers when someone rolls just short of the target but then someone remembers that they drew the copper coin.
"This coin can be used before a roll to grant advantage to anyone other than yourself."
The way this played out when I first started using these coins was great, so I saw no need to change silver's effect.
"This coin can be used before a roll to grant advantage on that roll."
I hesitated to make one coin directly better than another, but I felt the alternative to this was that it could only be used on the player's own rolls. While that might represent the concept of greed, which is usually associated with gold, I felt it wouldn't play out as well at the table.
"This coin can be used to change a roll to a natural 20. This effect may be used after the roll is made."
It doesn't grant advantage, so it doesn't interact with abilities that make use of that keyword, but the ability to turn any roll into a crit is obviously useful. Players tend to hesitate to use this one, though, wanting to save it for the perfect moment, which may never come. I've considered changing the effect to not make it crit, but that seems a bit overly-complicated.
"Flip this coin. The affected roll becomes a natural 1 or 20, depending on the result of the flip. This effect can be used after a roll is made."
This may seem directly worse than platinum's effect, but it can be used on any roll, even one made by the DM. Being able to take a party member's failed roll and make it either a crit, or a massive failure, is obviously cool, but being able to do the same to the BBEG's successful rolls is just as dramatic. I'm one of those GMs that house rules that natural 1s are fumbles, but you don't have to play this way for this coin's effect to still be fun.
"This coin can be used to grant disadvantage on any roll."
This effect is simple, but it seemed natural for the black electrum finish. Being able to screw over the bad guys is just as fun as being able to help your friends anyway, right?
I hope this write-up gives you some cool ideas for around the table. I'm also thinking of picking up some extras of these coins so I can adjust how common each coin would be when drawn at random, though there's something to be said for every player getting their own unique effect with no duplicates.