Here is the full list of all 18 Galcon Legends achievements.
Campaign completed at Cabin Boy or higher rank.
Campaign completed at Ensign or higher rank.
Campaign completed at Lieutenant or higher rank.
Campaign completed at Commander or higher rank.
Campaign completed at Captain or higher rank.
Campaign completed at Admiral or higher rank.
Campaign completed at 1-Stripe Admiral or higher rank.
Campaign completed at 2-Stripe Admiral or higher rank.
Campaign completed at 3-Stripe Admiral or higher rank.
Campaign completed at Grand Admiral rank.
Tutorial completed.
Defeated Walter.
Defeated Ms. Magpie.
Defeated the Crab Lord.
Defeated the Phantom.
Defeated the Banjo King.
Defeated Zanthor.
Defeated the Slug Princess.