Purchase stages
| Stage | Price | Prerequisite | Effect |
|---|---|---|---|
| Water Resistance 2 | 25 Pebbles | — | Engine floods after 10 s under water (8 s without the upgrade) |
| Water Resistance 3 | 50 Pebbles | Water Resistance 2 | Engine floods after 12 s under water (8 s without the upgrade) |
