Here is the full list of all 21 Timewalk Tower Defense achievements.
Win the game on normal mode.
Win the game on hard mode
Win the game on Impossible mode
Survive 5 waves in endless mode
Survive 10 waves in endless mode
Survive 15 waves in endless mode
Survive 20 waves in endless mode
Survive 25 waves in endless mode
Survive 30 waves in endless mode
Hit the same target 3 times with the same charge
Knockback the same enemy 5 times with Barricades
Hit a flying enemy with the direct impact of a fireball
Win a level with at least 5 conduits and never building mana wells
Have 10 landmines explode within 2 seconds of each other
Increase the attack rate of an Artillery to 0.5
Hit 15 units with a single air strike
Win a game while only building Attack Chopper Pads.
Get a Railgun to 1000 energy on the engineer.
Hit 12 enemies with the same energy beam.
Keep the scrap gun at full wind-up for 30 seconds
Have 25 bots alive at one time.