Only available in 15 card auto-daub rounds; each round has special blue-colored "Infinity Cards".
Getting a Bingo on an Infinity Card will award you a mystery box that can contain a piece of a Dauber. Collecting all the pieces of the Dauber will unlock it and its accompanying daily bonus increase. Once all the base Daubers for a given stage have been completed you will unlock the stage-specific "Mastery" Dauber.
Additional dauber pieces can be earned from Mystery Box Power Ups.