Here is the full list of all 38 Hammerwatch achievements.
Kill 2,500 enemies in the campaign
Solve it like it was E1M4
Get 10,000 coins in the campaign
Find the first easter egg
Kill the Queen on medium difficulty without having any crutches enabled
Kill the Knight on medium difficulty without having any crutches enabled
Kill the Lich on medium difficulty without having any crutches enabled
Kill the Dragon on medium difficulty without having any crutches enabled
Kill the Queen on hard difficulty without having any crutches enabled
Kill the Knight on hard difficulty without having any crutches enabled
Kill the Lich on hard difficulty without having any crutches enabled
Kill the Dragon on hard difficulty without having any crutches enabled
Find the second easter egg
Find the third easter egg
Find the fourth easter egg
Get 100,000 coins in the campaign
Get 1,000,000 coins in the campaign
Kill 25,000 enemies in the campaign
Kill 250,000 enemies in the campaign
Survive the castle collapsing
Kill the Crystal Lich in the survival level on medium difficulty without having any crutches enabled
Kill the Crystal Lich in the survival level on hard difficulty without having any crutches enabled
Air-walk between the start and the end!
Fail, where they fail: http://www.youtube.com/watch?v=-IAVCdu_DDs#t=467
Get combo kills until you reach 200
Get combo kills until you reach 1000
Kill the Dune Sharks on medium difficulty without having any crutches enabled
Kill Krilith on medium difficulty without having any crutches enabled
Kill Sha'Rand on medium difficulty without having any crutches enabled
Kill the Dune Sharks on hard difficulty without having any crutches enabled
Kill Krilith on hard difficulty without having any crutches enabled
Kill Sha'Rand on hard difficulty without having any crutches enabled
Complete the Temple campaign
Beat both the Castle Hammerwatch and the Temple of the Sun campaigns
It was better in the movie
Seriously?! That's what I got?
...is far away from the Green Hill Zone
Enter and exit the Pyramid of Fear