Here is the full list of all 39 Yrminsul achievements.
You've conquered 10 islands
50 towers on map
Collect 2500 infamy
Kill 500 foes
50 days of conquest
Collect 1000 infamy
25 towers on map
Hoard 300 Infamy
Kill 100 foes
You've conquered 20 islands
You've conquered 30 islands
7 Powers unlocked
All powers unlocked
6 towers unlocked
All towers unlocked
Hoard 1000 Infamy
Hoard 2000 Infamy
Collect 6000 infamy
Collect 10000 infamy
Collect 15000 infamy
Kill 1000 foes
Kill 5000 foes
Kill 10000 foes
Take the Seed of Health
Acquire the Seed of Plenty
Grab the Seed of Life
Claw the Seed of Peace
Complete the Death tree
Complete the War tree
Complete the Plague tree
Complete the Famine tree
100 towers on map
200 towers on map
350 towers on map
Thanks for playing through Yrminsul!
150 days of conquest
300 days of conquest
450 days of conquest
600 days of conquest