User blog comment:Lord Loss/Monster Appreciation Week: Baleful Gigginox/@comment-4697976-20130527011638/@comment-1837917-20130527115109

I think it has been stated that the Baleful Gigginox is in fact a mutation, not just a colour variation (which the genotypes P and p would actually work for: in fact, you could use those to describe Low and High rank Gigginox, since they have differing strengths of poison).

A mutation can occur by complete random, however there are numerous ways it can be induced. Inducement by radiation appeals to me (perhaps a Giggi that spent too much time exposed to UV rays?), but I don't think it could account for such a radical change in ailment production.

It may be just be one of those things in the MH universe where we have to suspend belief.