What does the 8 do in Shithead?
Verdict: in the official rules the 8 is invisible. It can be played on anything, counts as nothing, and the next player must beat whatever sits underneath it. A common alternative has the 8 skip the next player instead; a rarer one strips it of all powers.
Invisible, explained
Invisible eights are sneakier than they look. Play one on a king and the next player still needs a king or better. Stack three of them and the poor soul after you is answering a card they can barely remember. On an empty pile, an 8 is a free pass: the next player can play anything.
The skip version
Skipping is simpler and plays faster, and in a two-player game it effectively gives you another go, which some tables love and some consider cheating with extra steps.
The job swap
Some tables hand invisibility to the 3 instead, so the 3 does the vanishing and the 8 is just a card. Same trick, different uniform. We're aware of these people. Some of them are lovely. But the 8 has held this job in Harrogate for as long as anyone can remember, and we see no reason to restructure.
Our ruling
Invisible. It rewards memory and mischief, which is the whole game. If your table prefers the fast version, call it a house rule.