Here is the full list of all 21 Woah Dave! achievements.
Kill a rare alien!
Ride a UFO!
Let a Woah Block get blasted by a UFO!
Throw a Woah Block in the Lava!
Get killed by a UFO beam!
Defeat the mothership in Fort Bragg!
Kill a UFO!
Let two platforms get blasted by UFOs!
Collect one hundred pennies!
Kill 10 or more enemies with 1 Woah Block!
Destroy a Woah Block with another Woah Block!
Hit an Eyebat!
Earn your first penny!
Collect two hundred pennies!
Collect three hundred pennies!
Collect four hundred pennies!
Collect five hundred pennies!
Collect one thousand pennies!
Your name is POO!
Defeat the mothership in Peoria!
Defeat the mothership in West Haven!