This command would default to a d6 and support conventional RPG-style dice specifications, so usage would be like:
!roll !roll d10 !roll 2d20
Extra fun features:
https://todo.sr.ht/~nova/fletcher/61 tracks progress for the majority of the request, so I'll respond to the majority of this there. Thanks for the request!
For the pick outcome at random, this currently exists with the
!pickcommand (initial implementation at https://git.sr.ht/~nova/fletcher/commit/96ddae71446b11ae64557dc7444e81f9412dd4fd).