Subnautica: Below Zero Divethrough. Part 4 of 11. Mercury stern, Deep Purple Vents. Spiral Plants.

In which we
explore:
- the Mercury II stern for two parallel processing units
- the Deep Purple Vents for elusive Spiral Plants
acquire / build:
- moonpool
- fabricator module
- docking module
- booster tank
- depth upgrades 1 and 2 for Seatruck