Just for fun, I'll go ahead and throw in my own wildly uninformed speculation and conjecture, because goodness knows one can never find enough of it on the internet.
I'll assume it is indeed a special commemorative minifigure - we know it's a physical item, after all, and I don't think TLC would do a special production run of a whole discontinued set (or multiple discontinued sets) just for a two-day event, so I'm thinking it's something simple and small. It has to be something "nonessential," meaning something that there's not a huge demand for in a regular set - no major characters, say - yet at the same time have the sort of cachet to be a great fan-service item, and one recognizable to lots of the hardcore but not likely to appear in a set; this points to an EU character, one from some quasi-obscure tale(s) not frequently referenced today, yet appearing in something sufficiently well-known to be appreciable by a great many of the hardcore fans. This suggests a character from some really early EU production / publication. It also has to be something really distinctive, which suggests some new alien character, perhaps with a custom head element, yet at the same time, since it's just a promotional item offered for a brief time, it couldn't require some expensive new mold, so it must be entirely made of existing LEGO elements, but perhaps ones no longer in regular production, and / or in different colors than before, and ideally, something that could make use of colors heavily represented in the current production palette, such as one of the dominant hues in the Power Miners line.
The answer, then, is quite clear: it's obviously
minifig, using the Nesquik Bunny headpiece
in lime green. You're all welcome.