I've had many a nethack run end due to mimics :/
My first thought indeed! Though I don't have quite as much trouble with them (I can tell where they are in Sokoban now and generally don't fall for them in the store), they can still be a nasty shock.
They aren't too bad once you are more tooled up but early game they can be a swift end to a run if you aren't playing well.
I also think you meant "Sokoban" not Sudoku.
What? Huh? I never said that! *whistles innocently*
As a side note, I'm actually rather amused that, for the most part, in video game circles, the word "Mimic" is often instantly associated with fake treasure chests. Somehow that seems odd to me.
Valve had a great idea, they painted them black and turned them into these.
There's a few of those in Metroid Fusion.
They look like missile and energy expansions then you go to get them and... they're enemies.
They don't one-hit kill you but they're still a nuisance.
Not sure if anyone has said it yet but the Electrodes and Voltorbs from Pokemon would fit the bill for this.
There were also mimics in Castlevania.