Here is the full list of all 20 Gamble Tower achievements.
Find the Gambler on the "top" of the tower.
Defeat Eskyuven.
Defeat Noxaerudeux.
Burn Magic Spark while having 0 mana.
End the expedition in Success once
Defeat the Orbots.
Burn an Aseptic orb.
Accumulate 5000 Gold.
Accumulate 10.000 Gold.
Accumulate 50.000 Gold.
Accumulate 100.000 Gold.
Spend 1000 Chips on Stebax.
End the expedition in Success 5 times.
End the expedition in Success 20 times.
End the expedition in Success 50 times.
Reach max level with every clan.
Unlock every single unlockable on the Unlockable List.
Find the Janitor.
Survive an encounter with less than 10 HP.
Finish a combat while losing 3 Gambles.