Mithridates VI of Pontus' Cup

Origin
Mithradites was king of Pontus who engaged in several wars against the Roman Republic and its generals Sulla, Lucullus and Pompey the Great.

An antidote to all poisons, mithradite, was supposedly created by Mithradite to prevent an assassination attempt by poisoning. He was said to have lived in the forest for some time and developed a tolerance to poisons by habitually swallowing semi-deadly doses so his body could get used to them

Effects
When it touches any plant, said plant will become poisonous. When it touches the skin, the poison will cause severe allergic reactions and almost complete loss of motor control.

Interestingly, it is noted to make those affected the cup virtually immune to all other poisons, whether metallic or organic.

It does not react well when near Sulla’s Grass Crown or Pompey the Great's Shield, so it had to be shelved away from the two.