Skeleton mages are monsters found in the Waterfall dungeon. When they target to attack a player, they start by saying "i infect your body with rot", which casts a magic spell on them that resembles Confuse, Weaken, and Curse, as it lowers their Attack, Strength, and Defense levels by 5%.
It is important to note that even if the monster does not end up fighting the player, as there are other aggressive monsters in the dungeon such as Skeletons and Shadow spiders, they leave them weakened by casting the spell before engaging in melee combat.
This article on a monster has an associated dialogue page.
All herbs are dropped in Unidentified form.