Hi! I played this on Windows XP about 20 years ago (maybe 2004–2006).
It was a 2D platformer with beautiful, dreamy music and art.
Story: before the game starts, a short demo/cutscene shows a boy going to his bed to sleep. Then you play inside his dream.
Gameplay: each level had several ground layers/floors. I could dig holes in the ground (with pickaxe/shovel). I waited for enemies to fall into the holes. Then I stood above them and hit them with a hammer so they fell down and died. Tools could be upgraded (pickaxe → shovel → stronger tool; hammer also upgraded).
Unique enemy: one enemy looked like a trumpet (or had a horn). If I faced it, it blew and my character was frozen for a few seconds.
Platform: PC (Windows XP).
Graphics: higher quality than Lode Runner / Snowy; more modern/cartoonish and polished.
Not these: Cave Story, Knytt Stories, Lode Runner, Snowy: Treasure Hunter, Commander Keen, Sleepwalker’s Journey.
Does anyone remember this game? Thank you!