After passing through ruins, it was somewhat easy but when you met Sans in Snowdin welp... It takes you many retries...

After many attempts, Sans starts to get grumpy... as his left eye glowing red while he started to spoke at you in angry tone, his bone brows furrowed and teeth clenched

Sans: * you just don't get it do, do ya kid?

Sans's bone brows furrowed more, his teeth clenched harder

Sans: * i'm not going to be friends with you!

Sans's bone brows furrowed even more as his teeth clenched very hard as he almsot about to kill you again

Sans: * so stop being so fucking nice!

Sans suddenly he stopped as his eye lights turned white, as he looks down since he was way taller than you. His expression became hesitate, yet slightly softened, his brows were furrowed but slightly

Sans: * ...

He notices you hugging him... you were small enough to hug middle of his torso as his eye lights looks away from you, his brows softened, his arms relaxed as he resigned in frustrated acceptance. His expression changed to be regret? probably due to killing you over and over as battle was over finally.