Mabinogi, aside from having a bit of an alphabet soup name, is not a game known for holding things back until the next content update. If they can think of something neat to add in, they'll happily do so more often than not. So it's not exactly a surprise that with their upcoming Alchemist update, focused around (wait for it) the Alchemist, the game will be adding brand-new "Shadow Missions" as well.
The official site has a small preview with a list of mission types for what looks to be an interesting addition to Mabinogi's gameplay.
"Today, leading game publisher Nexon announced its venerable free-to-play fantasy MMORPG "Mabinogi" will be celebrating its 14th anniversary on March 27th, 2022." - Nexon.
"Leading game developer Nexon today announced that they have just released the second update to the "Stardust" saga for their F2P fantasy MMORPG “Mabinogi." - Jonas Ek, TGG.
"Leading game developer Nexon has announced the newest Stardust update for its free-to-play fantasy MMORPG "Mabinogi". Beginning today, Milletians will be introduced to the latest non-playable character (NPC) Melwyn, who will award players with materials to unlock mystical Stardust skills. Players will also be able to participate in the challenging Shadow Missions and new Intermediate Dungeon Levels." - Nexon
This looks good, and the studio was created by the original Arkane Studios head, so it should be in good hands.