Pygmy Oil

Drinking Pygmy Oil does indeed make you smaller, but not really small - at least not if you stop at one. Each oil you drink will make you incrementally smaller. This skrinkage lasts for 10 minutes.

Drink a number of Pymgy Oils, and you turned into a Pygmy! This is basically a gnome with the old witchdoctor style mask. The number of oils required to drink for this buff varies, but it usually 8-10. Pygmification last for 10 minutes. You are able to mount while pygmified, unlike many shapeshifting buffs.

Pygmy Oil is also a reagent in a number of alchemist made items, including flasks and an alchemists stone.

Pygmy oil is made by alchemists, who create 1-2 oils per Pygmy Suckerfish. Most if not all alchemists should be able to create these oils, as it's trained early in Northrend.

Pygmy Suckerfish are freshwater parasites, and are sometimes found attached to fish caught in open inland water in Northrend (except in Dalaran).

Alice (in Wonderland) drank from a bottle marked "Drink me." The more she drank, the smaller she became. She also ate a cookie marked "Eat me." which had the opposite effect - the more she ate the larger she became. Something to watch out for!

Gnome+this in a battleground: nobody can target you.

Spoiler

Not even the healer.

"Eat Me" is already in use by Savory Deviate Delight. I would say that Pygmy Oil was the one to watch for...
As far as growing goes.... Winterfall Firewater has done this but only in single doses. What happens if you use the Pygmy Oil AND the Firewater?