Charlie Sheen -- Mystery Alaska ... I'm Hunting a Half-Otter Man -

Barely a month after his Loch Ness monster mission failed, Charlie Sheen is back on the hunt for crazy mythological creatures ... this time in snowy, snowy Alaska ... Charlie's favorite.

Charlie tells TMZ, he flew up to Sitka, AK on his private jet last week in search of the mythic Kushtaka, which loosely translates to "Land otter man."

Stories about the elusive Kushtaka originated among natives in Southeastern Alaska ... and according to Charlie, it's "a shape-shifting trickster who is half man, half otter. It lures one away from the campsite with the mimicked sounds of a crying baby, then kills you, takes on YOUR form, and returns to the scene for more suckers or prey."

Charlie says he embarked into the wilderness with some friends in order to find the creature ... but just like on his Nessie mission, he returned empty-handed. Sheen has since flown back to civilization.

Charlie tells us, "It obviously knew our group was far too skilled to be snowed in this fashion so it stayed hidden like a sissy."

Yeah, that's what happened.