Unlock expert mode:
Complete every level with all three submarines.
Unlock Chapter 6:
Complete Chapters 1 through 5 with all three submarines.
Unlock Chapter 7:
Complete Chapter 6 with all three submarines.
Decal Effects:
Collect the specified amount of the listed decal to unlock the corresponding effect:
DECAL – EFFECT
1. No decal – Default.
2. Anchor (3 required) – Halves damage taken from collisions with the environment.
3. Octopus ( 3 required) – Halves damage taken from enemy torpedoes.
4. Skull and Crossbones ( 3 required) – Halves damage taken from enemy depth charges.
5. Arrow through Heart (5 required) – Halves damage taken from collisions with enemy vessels.
6. Swords and Shield (5 required) – Halves damage taken from mines.
7. Wooden Ship (5 required) – Quadruples recovery speed at the water’s surface.
8. Bomber (3 required) – Halves damage taken from enemy air-to-sea bombs.
9. Snail (7 required) – Reduces damage taken from all sources.
10. Orca (3 required) – Halves air consumption rate of the masker.
11. Lobster (5 required) – Prevents submarine hull leaks.
12. Bull (7 required) – Increases torpedo damage.
13. Golden Falcon (10 required) – Increases maximum forward/reverse speed.
14. Sea Serpent (7 required) – Increases maximum dive/surface speed.
15. Eye (5 required) – Reveals enemy positions on the sea chart.
16. Tridents (7 required) – Increases torpedo reload speed.
17. Lightning (5 required) – Increase torpedo travel speed.
18. Crescent Moon (5 required) – Extends the mission time limit by 60 seconds.
19. Scope Orb (7 required) – Extends post-mission Periscope Strike by 10 seconds.
20. Cherries (10 required) – Extends post-mission Periscope Strike by 20 seconds.
21. Sun (10 required) – Increases torpedo speed in post-mission Periscope Strike.
22. Panther (10 required) – Decreases enemy speed in post-mission Periscope Strike.
23. Crown (10 required) – Lowers the health of enemy bosses.
24. Scorpion (5 required) – Negates the effect of water currents.
25. Squid (3 required) – Increases the effect of waters currents.
26. Sea Horse (3 required) – Halves the effect of water currents.
27. Penguin (7 required) – Halves the impact of shock waves.
28. Wave (10 required) – Grants a one-time health boost when reduced to zero health.
29. Frog (3 required) – Increases the impact of shock waves.
30. Fire (3 required) – Increase the amount of bubbles created by your torpedoes.
31. Mario (10 required) – Homing torpedoes.
32. Whale (10 required) – Become a whale.