ArenaNet has posted a rewards calendar for Guild Wars which features a variety of tasty tonics.

In the first scheduled update of every month, one new flavor of the ever-popular transmogrifier tonics will be added to the Zaishen Chest, replacing the tonic from the month before. These special tonics, usable only in outposts and towns, will transform your character into the embodiment of that particular potion.

Open the chest for a chance to find one of these special tonics. If you're very lucky, you may even find an Everlasting tonic. These super rare variations have infinite uses, so they'll never run out.