Mammoth's Moss

Mammoth Moss is a greenish brown moss that grows in warm/wet hollows between rocks, usually near natural mountain hot springs. Due to it's specific atmospheric requirements, it is a very rare, and even more rare because it is particularly loved by many animals in northern climates, and so much is eaten before it is found by civilized peoples.
When brewed into a tea, the tea will have a number of effects on the consumer. They will grow fur all over their body, and grow tusks from their mouth. They will also increase significantly in size, sometimes by many feet, as well as grow larger muscles to compensate. The effects can last for many hours, and Mammoth's Moss tea is highly sought after by Northern warriors to boost their abilities in battle, as well as a survival item when traversing hostile cold-weather environments. For many, a cup of Mammoth's Moss tea could be the difference when facing a sabre-tooth tiger or other predator of the North.
Mammoth's Moss is mostly found in Northern climates, but can also be found in rare occasions in other places, where it's specific growth requirements are met.

Mechanically, drinking a cup of Mammoth's Moss Tea will increase your size category by 1, increase your STR score by 2 (over twenty is possible), give you resistance to Cold and Slashing Damage, and increase your total HP by 1d12 per 4 levels of the drinking character. 
the effects last for 1d6 hours, increasing to 1d8 if used by a Druid.