When you've been stuck on the Sans boss fight for so long, that you

nothing useful. — Sans' Battle Dialogue Explained

SANS is starting to get tired : r/Undertale

Asgore Dreemurr, Undertale Wiki

The 24 best free video games to play while you're stuck at home

Stuck on the sans encounter does anyone know how to beat this? : r/Undertale

nothing useful. — The “bad time” is more than Sans' battle

Stuck on the sans encounter does anyone know how to beat this? : r/Undertale

JadeMaster!Sans (Original), The Lunar Verse Wiki

After so long, I beat sans only took like 6 hours. : r/Undertale

Undertale] Sans' boss fight - Genocide Run

sans is not and never will be as hard as people say he is : r/Undertale

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Boss Guide - Undertale Guide - IGN