Here is the full list of all 35 Nectarmare achievements.
Make it through the last level
Tried out a level in challengemode
Won the first 20 levels
Won 40 levels
Beat level 26 with the enemy taking 0 points
Beat level 32 with the enemy taking 0 points
Beat level 11 with the enemy taking 0 points
Beat level 46 with the enemy taking 0 points
Beat level 42 with the enemy taking 0 points
Beat level 7 with the enemy taking 0 points
Beat level 16 with the enemy taking 0 points
3000+ points in challengemode on the 20 first levels
3000+ points in challengemode on the 40 first levels
3000+ points in challengemode on all levels
Lose no lives on the first 20 levels
Lose no lives on the first 40 levels
Lose no lives on all levels
Beat level 51 with the enemy taking 0 points
Have more than 6 Centipedes appear when fighting the Boss
Avoid getting stuck when 6 or more webs are active
Have at least 6 Hazardseeds active at the same time
Blocked damage from the Grasshopper with the booster
Blocked damage from the flymissile with the booster
Blocked damage from the centipede with the booster
Blocked damage from the fish with the booster
The enemy picked up more than 8 points
Have the Boss missile hit and kill a creep
Have the Spiders missile kill a creep
Have the Eyeflowers missile hit and kill a creep
Have 3 creeps get stuck in the same spider net
Kill a creep with a bomb
Get 5000 points or moore in challengemode on a level on map 3
Got 9000 points or moore in challengemode
Have the frog hit the enemy with its tongue
Beat level 47 with the enemy taking 0 points