This comic follows on from the Previous comic which will almost certainly provide context.
The spell Konsi's talking about is "Fortune's Favour" - it's level 2, consumes a 100gp pearl to cast, and lets you re-roll a single D20 within the next hour. It's in Explorer's Guide to Wildmount.
It's been a little while due to drawtober, and my website is (mostly) functional again, so if you want to read all the Konsi comics from the beginning, you can do so on my website at this link. Please be advised that these posts are presented in reverse chronological order, so start at the end and work backwards.
@ahdok
I think I am going to steal that rule for my campaign