Here is the full list of all 15 Selknam Defense achievements.
Raise all units to level 3.
Beat the 7 minutes and 29 seconds on survival mode.
You found a crude reality.
You defeated the evil boss.
Discover the genuine evil.
Unblock the survival mode.
Reach at least eight buffed selknams at the same time.
Kill five enemies using only poison.
Confuse, stun and catch with a network the same enemy.
Pass one of the level from second world and above, on triple speed.
Raise a complete class of Selknams to level 3 (archers, bowlers, warriors or mages).
Sell a unit that is almost dead.
Resist a suicide explosion with your Selknam tank preventing your allies death.
Switch position between two units.
Complete the three first levels on campaign mode, obtaining nine stars.