Because of the day (Friday 13th) and I live in the New York area, I feel this is a fun exercise. If others have done this; I apologize. Right now I need a creative avenue. 

Still editing but with the end of the night approaching, I feel I need to post this now to make good on the date.  Please comment. I will review and consider and adjust below.  Still working on links, so my apologies on that. Not a good excuse, but the reason is I started this late and wanted to post on the 13th. So I do apologize for incomplete formatting and grammar. Also,I am not best with with calculating CR ratings: so I left that open until I get opinions on the design of the character. I will attempt when I think comments reviewed and consider. One note: I want to avoid conscience magic abilities. So no direct spells; but an implied spell feature is okay. Overall....I just want to have fun due to the date.  So please, give me your comments. Thank you and have a great weekend....and have FUN!

Jason Voorhees 

Armor Class 15 (natural armor)
Hit Points 218 (19d12 + 95)
Speed 30 ft.

STR              DEX           CON           INT              WIS               CHA
20 (+5)       11 (+0)      20 (+5)      12 (+1)       16 (+3)         18 (+4) 

Saving Throws DEX +6, WIS +9, CHA +10
Skills: Perception +9, Stealth +6

Condition Immunities Charmed, Exhaustion, Frightened, Poisoned

Senses Darkvision 120 ft., Passive Perception 13

Languages Common (cannot speak)

Challenge TBD                                 Proficiency Bonus +6

Damage Resistance. Jason has resistance to bludgeoning, piercing, and slashing from non-magical weapons.

Legendary Resistance (3/Day). If Jason fails a saving throw, he can choose to succeed instead.

Natural Armor. Jason’s natural armor is AC15 provided he does not don any armor (else his AC is equal to that of the armor’s AC).  He is not proficient with a shield.  If his DEX or CON score increases or decreases from the listed stats then his AC adjusts according to reflect the sum of the DEX and CON modifiers plus 10.

Proficiency Attacker. Jason is proficient is using all simple, martial, and improvised melee weapons and weapons with the Thrown property. Jason is also proficient with the hand crossbow. Jason can wield one-handed weapons that lack the light property in each hand.

Regeneration. Jason regains 20 hit points at the start of his turn if he has at least 1 hit point. If Jason drops to 0 hit points then he gains 21 temporary hit points at the start of his turn.  If Jason takes over 199 points of damage before gaining temporary hit points then he is destroyed.

Eerie Presence. A aura of undeath and dread spreads from Jason which corrupts the ground surrounding him. The area within 60ft of Jason is consider difficult terrain.  If a character attempts to Dash in this area they must succeed on a DEX saving throw (DC 18) or fall prone after 20ft of movement. Jason is immune to this effect.

Jason Weaknesses. Jason has the following flaws:

Harmed by Running Water. Jason takes 20 acid damage if he ends his turn in running water.

He Wasn't a Very Good Swimmer. If Jason is submerged by water he is incapacitated, Jason is paralyzed until his head breaches the water.

A Mother’s Special Boy. A creature may attempt to trick Jason by addressing him with a message under the guise of "His Mother’s Insistence".  This can be through showing Jason a trinket associated with his mother, reiterating a phrase his mother used, or pretending to be his mother. The creature makes a skill contest at disadvantage against Jason’s Perception. If the creature succeeds then Jason is incapacitated. The creature may attempt to direct Jason to take an action, similar to the Suggestion spell, by performing another contest.  If the creature succeeds again, Jason will proceed to perform the action.  If the creature or any their companions attack or cast any spell on Jason or 1 minute passes without Jason seeing the source of "His Mother’s Insistence” then the he reverts to his free will and is immune from the creature attempting to influence him again for seven days. 

Attentive Stalker. When a creature uses the Dash action, Jason’s focus is shifted to the creature and must use his action to pursue the creature. Once Jason is within 5ft of the creature he cannot use any other action. This feature cannot take affect on consecutive rounds.

Actions

Multiattack. Jason makes three attacks with a weapon,  Aggressive Grapple,  or Throw.

Longsword Weapon (default). Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 9 (1d8 + 5) slashing damage, or 10 (1d10 + 5) slashing damage if used with two hands, plus 18 (4d8) necrotic damage.

Alternate Weapon. Melee Weapon Attack: +11 to hit, reach based weapon definition in Players Handbook, one target. Hit: based off damage of weapons defined in Players Handbook plus 14 (4d6) necrotic damage.

Aggressive Grapple. When using multiattack, Jason has advantage in a contest to Grapple a creature that is consider Large or smaller. 

Throw. If a creature is grappled then Jason may throw the creature 20ft. When the creature lands it is prone. If the creature hits a solid object like a wall or tree prior to travleing 20ft then it takes bludgeoning damage equal to a d4 roll of twenty minus the distance traveled. For example, the creature is thrown and hits a wall within five feet; the creature takes twenty minus five or 15d4 (37) points of bludgeoning damage. 

There is Nothing There. Jason can shift through the shadows and hide from any creatures' vision. He can use Disengage, Dash, and Hide as a single action. Jason gains advantage on his next attack and creatures cannot attack him until the start of his next turn. 

Reactions

Parry. Jason adds 6 to its AC against one melee attack that would hit it. To do so, Jason must see the attacker. If the attacker misses then Jason can attempt a regular grapple contest. If Jason succeeds then the attacker is grappled and cannot make additional attacks on the same turn where the melee attack missed.

Bonus Actions

Ki ki ki, ma ma ma……(6/Day). Jason enters into a serene state of bottled up rage.  All damage rolls apply a +4. If Jason does not make a multiattack for his turn then the rage ends and he cannot use this again until the start of his next turn.

Legendary Actions

Jason can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. Jason regains spent legendary actions at the start of its turn.

Move. Jason moves up to its speed without provoking opportunity attacks.

Weapon Attack. Jason can make one weapon attack.

There is Nothing There. Jason can take this action to conceal himself until his next attack.

Grapple and Throw (Costs 2 Actions). Jason attempts a grapple contest and if successful can Throw the creature.

Only note I have is see if you can find the UA Revenant species/lineage, not the UA that eventually became the Reborn, but the Revenant.  If you use that as a template, I believe you'll have a lot of features you wouldn't necessarily have to generate from scratch.

This is the first (and very well timed) monstrous homebrew I've seen for spooky season and I think it's fun.,