honestly, just memorize his attacks.
stock up on food
what helped my friends in practice on bad time simulator
and don't eat until phase 2, no matter how low ur health gets.
I suggest getting all 3 snow pisces, leg heros, butterscotch pie, face steak, and ab. quiche.
also don't equip the real knife uc u don't need it. even when you hit sans at the end, ur guaranteed to one-shot him. equip a weapon that'll raise ur def. or use the torn notebook. itll increase ur time for being invincible after u get hit and itl raise ur def.