People who have avoided spoilers or have never even heard of the game who are now for the first time ever playing Undertale should have basic knowledge of it?
(Deleted the last comment because of grammatical error :p)
Ah yes, the final boss.
Looks like everyone else got it covered. Food enough and memorize the patterns.
Break as needed.
Unfortunately, you have to fight him
Bring lots of food. If your LV is low, I suggest bicycles because you get 2 uses out of them. Eventually, you’ll memorize his attack patterns. Just keep trying, you’ll get it in time.