CR for 5e homebrew monsters

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Im a fairly new DM. For the most part i think im doing well, but im having trouble figuring out what i should have the CR listed on my homebrew monsters. how do you guys determine the CR of your mobs. also what do you think the CR of this would be.
Bleeding hatebeast
Huge demon
Chaotic evil
Movespeed: 35ft
Str:28 (9)
Dex:10 (0)
Con:20 (5)
Int:1 (-4)
Wis:1 (-4)
Cha:0 (-5)
Save throws: str+14, con +12,
HP:300
AC:11
Immunity: fear, charm, prone, exhaustion
Resistance: Bludgeoning, piercing, slashing from non magic weapons
Senses: passive 6
Skills: Grapple +10
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Multi attack: hatebeast can make 2 attacks
Endless claws:+9 to hit, Makes 5 claw attacks (2D4+9)x5 / slashing/ 10ft reach/
Mindless clawing:+9 to hit, make a claw attack vs every creature within 10ft. (2D12+5) /slashing/
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Multi-Headed: Each time the hatebeast becomes dazed or stunned, it loses one attack on its next turn instead. Multiple such effects stack
Unstable flesh: Take 1D10 damage each turn
Nightmare of flesh: creatures within 5ft must roll a DC12 wis save, on fail roll from the short term insanity table
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