Here is the full list of all 40 Jets'n'Guns 2 achievements.
Completing your first item set.
Save the sledger before the tragic end.
Collect 100 gift packages in Xmas Mayhem level.
Find secret Xmas Mayhem level.
Defeating Necrodroid Titan from Moon Colony.
Defeating Techno-Kraken from Water World.
Defeating Kong 25 - Panzer Devastator from Pirate Base.
Defeating RX-TDY Jet Fighter from Star City 17.