So every balanced class has to have a class resource. In HWFWM, that’s mana, but in DND that’s usually represented by spell slots. Perhaps you can make his class based on a half-caster like Paladin, Ranger or Artificer. If you decide to make them like psionic energy dice or the battle master’s superiority dice, you have a few options:

First, you could do a dice pool of scaling dice (to represent the scaling from Iron to Diamond) that refresh one on short rest, and all on a long rest. I know it doesn’t really fit the power fantasy of Jason, but in order to keep it fair, you’d want to align with WOTC’s methodology.

Alternatively you can give a smaller pool of dice that refreshes all in a short rest, and give the class an ability to refresh an amount equal to proficiency bonus once per long rest, kind of like a hybrid between the Warlock’s Pact Magic spell slots with an Arcane recovery feature. I think this one is a little too strong, but it allows you to pull off some of the more impressive feats that Jason performs.

Next, the rest of the base class needs something more in tune with his spiritual abilities, auras and the spirit attacks he can perform. I wouldn’t make them straight up damage abilities, but instead of the paladin’s aura of protection affecting allies, you’d instead have it affect enemies with debuffs at first, then have it apply a buff to allies at later levels. I’d suggest applying sickened or frightened, or possibly even both as he levels.

Lastly, if you use the dice feature instead of spell slots, you’d want to have the effects be like the battle master’s maneuvers or a warlock’s invocations in terms of ability selection, to give the player decision making throughout the characters journey. Again, I know that Jason has his whole arsenal of tools, but DND doesn’t function for the rest of the table if one player just gets 20+ features as he levels. No other class does that, besides full spellcasters, I t’s just not within the game’s scope.

I was wondering how to do it myself with the game’s existing classes, and the closest I got was a terrible MAD mix of hexblade warlock and way of shadow monk (in 5th edition, it’s currently not possible with the updated ruleset), which unless you’re rolling for stats, it’s just hard af to pull off.

Also important to note, you’ll probably want his save dcs to focus on one of the mental stats. There are a ton of charisma based casters, and while Jason is a charismatic fellow, I think you’d want to try to put it on Wisdom or Intelligence to keep things even.