Here is the full list of all 12 Spoids achievements.
Earn a Platinum medal or better on all missions.
Earn a Gold medal or better on all missions.
Complete all of the missions.
Earn a Silver medal or better on all missions.
Build 500 unrecycled towers.
Have a single tower destroy more than 100 Spoids in a mission.
Have a tower occupy every available spot on a mission.
Last 15 minutes in an infinite wave mode mission.
Complete a mission with fliers using no Homing Missile towers.
Change the targeting priority of 5 different towers in a mission.
Complete the Defense Training mission.
Complete a mission using zero EMP towers.