往死里 is basically an intensifier here. It implies extreme violence or murderous intent. It's often used for hyperbole.

An intensifer, exaggeration to mean "very". Literally "towards death". However, the meaning changes depending on what comes next. For example, 往死里投生, lit. through death and survived, i.e. a harrowing escape or survival after a castastrophe. 往死里打 = beat until you go to hell, i.e. beat till you die.

It's an adverb. It means "without mercy".

Beat you to death = 往死里打

It means someone to do something heading the extreme situation. 往死里打 means beat (someone) until he die. You can change the last character to any verb to describe any other action . Such as 往死里说 ， 往死里玩， 往死里做， 往死里爱. But 往死里打 is more comment. Sometimes it's a funny expression. Pay attention to the tone.