I keep all my figures (and dolls) in plastic Ziploc bags, which turned out not to be such a good idea:
The plastic costume accessories of this Monster High figure reacted with the plastic of the bag, resulting in destructive "melt." Several bags ended up plastic-welded together. Fortunately only the one figure was affected.
The pink goo that now looks like disemboweled intestines used to look like nautical chains. I must admit, though, that strings of intestines are creepier than chains, so it wasn't a total loss.
Only the pink plastic seemed to be affected. The figure had been bagged up for about three years.