The word is used in reference to the marketing of toys or collectibles I believe.
Question was kind of sparse, but here’s a guess. “Chaser” is usually, in America at least, a term of any liquid that immediately follows a straight shot of liquor.
Making an assumption, I would guess that your OP refers to anything that follows up a marketing ploy. i.e. Ken after Barbie, fast-food promotional tie-ins, books based on popular movies/books, etc.
A “chase” in terms of collectable toys is a small run of a certain toy that differs from the more widely available version.
Sometimes its because of a mistake that was corrected and sometimes they’re done on purpose and insterted into shipments as a ‘prize’ for people to find.
McFarlane toys does this a lot right now with their sports figures. They will paint a player in his team’s white uniform, but then release and randomly distribute a few thousand of the player wearing his team’s coloured jersey.
Everyonce in a while you’ll find the mistakes too. They range from everything to Darth Vader being put in the box before his helmet was fully assembled, to Barbie being packaged upside down.