Here is the full list of all 35 Love is Dead achievements.
Find a Photograph
Beat a level with 3 Pancakes
Completed the World 1 Finale
Completed the World 2 Finale
Completed the World 3 Finale
Completed the World 4 Finale
Completed the World 5 Finale
Completed the World 6 Finale
Completed the World 7 Finale
Find Your Pets
Complete a Zoo Level
Complete a Trap Level
Complete a Smorgasbord Level
Complete a Camerabooth Level
Complete a Pancake House Level
Complete a Gauntlet Level
Find 10 Photographs
Find Every Photograph
Collect 213 Pancakes
Find a Secret Exit
Zombify the Mad Scientist
Paint Pictures for the Pirates
Knock down every skull in Level 1-2
Flatten enemies with cars 10 times (friendly zombies do not count, must start the car yourself)
Paint and sculpt 250 pieces of art
Blow up 6 Pirate Lackeys with your own cannonballs
Zombify every Spearhuman and Bowhuman in Level 5-5 (they MUST be eaten, they cannot blow up unless they've already been eaten)
Free a human from stasis
Two cone heads fall in love
Two shy zombies fall in love
Two artists fall in love
Two painted works of art fall in love
Two overcaffeinated zombies fall in love
Two batteries fall in love
Two star zombies fall in love