The Mysterious Man is an NPC with 1000 health that can be found on the layers of Vethea. When double right-clicked, he will give you a number of Lumps, the tier of which depends on the level in which they are located. For example, the first layer gives three Teaker Lumps while the second gives six Darven Lumps, and the third ten Pardimal Lumps. Lumps are used to create weapons and armor using an Infusion Table.
The first Mysterious Man, on layer 1, is red.
The second, on layer 2, is green.
The third, on layer 3, is blue.
There are other NPC's, such as the Crypt Keeper, who give other lumps, like the Arthrimis Lumps, but the high-tier ones are boss drops, matching their boss.