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