Outside of the Bard's Bardic Inspiration, what abilities or spells currently exist that give a die to another character to use for anything combat related? I can only think of the Bless spell and the Guidance cantrip. I am thinking of creating a subclass that uses dice as a combo mechanic. Are there other examples?
The Resistance cantrip also gives a d4, it helps with saving throws. At the meta level, a DM can give an inspiration to someone that lets them reroll on anything. This is usually provided for good rp or fun moments.
Battle Master Fighters can do a Commander Strike and add a d10 to the damage, though that's so quick after the rolls I don't know if handing over dice is worth it.
I had a DM once that liked offering inspiration not as a one time advantage, but as a d4 that could be collected and used piecemeal. So you could get more then one d4 of inspiration at a time, and decide to use one or more on any d20 roll. It was a fun way to give inspiration, especially at lower levels where a d4 is still super useful but not as super-powered as straight advantage.