Poison Stones are upgrade materials in Dark Souls II.

In-Game Description

An altered state of titanite.
Used to imbue weapon with poison or to provide poison reduction to shields.
Sorcerers at the Melfian academy once attempted to imbue titanite with various elements, but are said to have failed. Someone must have succeeded though; what else would explain this stone?


Given to Steady Hand McDuff along with souls to infuse a weapon with poison damage. Not all weapons can be infused with poison.