Path of the Hulk

You are an intellectual by trade and you focus most of your time trying to make advancements in these areas and preserving life.  However, one day your curiosity finally caught up with you - and your tampering with the natural sciences wasn't exactly the wisest thing you have done.  You were infused with an unknown mix of chemicals and radioactivity causing mutations at the genetic level giving you the ability to become a single, monstrous beast when you rage.  You spent a lot of time being angry, fighting the world, and transforming back and forth between yourself and the beast. You started down the path of The Hulk when you began being able to control your more combative nature.

Roleplay suggestions:  I chose Barbarian class for simplicity purposes - to expedite game play at the table.  This is why the first ability you get in the path is ability is Strength for Int-based checks.  This is fairly straightforward and while not in combat, I would roleplay a normal creature.  When initiative starts, just rp them changing instantly changing into a medium sized combat focused beast.  Then something happens that enrages them even further making them grow in size.

Brilliant Genius

You are really a genius and your strength is actually your intellect while you aren't a combative beast.  It's what helped you determine the trick to keeping the beast inside quiet is to always be angry and keep your cool.  While you are not raging and out of combat, you gain the following benefits:

• You have advantage on  saving throws against being charmed or frightened.
• You may use a Strength check instead of Intelligence when performing Intelligence ability checks.  (This override is done in the character sheet).

This feature improves at level 10 and again at level 20 of this class,

Hulk Out

You have learned to use whatever is at your disposal when fighting and your rage turns you into a beastly humanoid creature.  You gain proficiency with improvised weapons.  Strength based attacks using your unarmed strikes and improvised weapons do 1d8 damage when you are wielding a shield and 1d12 damage when you aren't.

When you take damage, you may use your reaction to expend one use of your rage to begin raging and then apply the damage. While raging you gain the following benefits:

• You grow up to 5 feet taller and you count as two size categories larger when determining your carrying capacity and the weight you can push, drag, or lift
• Your jump distance is tripled and you gain a climb speed equal to your walking speed
• When you hit a creature with a melee attack you may use a bonus action to attempt to grapple the creature
• You have resistance to fire, cold, thunder, force and radiant damage

Thunderous Beast

Your ungodly strength creates ripples in the air when you attack and lets you treat creatures like toys, using them as improvised weapons to toss around or pummel endlessly.     Your unarmed strikes and attacks with improvised weapons count as magical for the purposes of overcoming resistances.

In addition, you may perform one of the following attacks as an action while raging.  You may choose a different action each time you use this feature:

• Thunderclap: You clap your hands and creature a thunderous wave of air forming a line 100 feet long and 5 feet wide that blasts out from you in a direction you choose.  Each creature in the line must make a Dexterity saving throw.  On a failed their save, a creature takes 4d8 thunder damage and is knocked prone and pushed up to 10 feet away from you. On a successful save, a creature takes half as much damage and isn’t knocked prone or pushed.  The wave puts out any fires within 5 ft of its path and any nonmagical objects in the spells path that aren't being worn or carried take maximum damage.
• Puny Mortal: You wield a creature that you have grappled as an improvised weapon with 20/60 ft thrown range.  The creature must be your size or smaller.  Make an attack against a creature or object.  If you hit, both the target and the grappled creature take 1d12 + strength modifier + proficiency bonus damage.  If you made a melee attack, you may throw the grappled creature at the end of the attack, placing them in an unoccupied square within 60 ft. Enemies within 30 ft that can see you must take a wisdom saving throw.  On a failed save, they are frightened of you for one minute.  They may make an additional save against this affect at the end of each of their turns.  The creature you used as an improvised weapon makes their first saving throw with disadvantage.

The DC for this feature equals 8 + your proficiency bonus + your Constitution modifier.  Once you use this feature, you cannot use it again until you finish a short or long rest.

Brilliant Genius

At 10th level, you have perfected your scientific studies.  While you are not raging and out of combat, you gain the following benefits:

• You may add your proficiency bonus when you use your Brilliant Genius even if you are already proficient with the skill.
• You may also cast Legend Lore at-will without components.

When you reach level 20 in this class, you have mastered how to merge your two personalities and your brilliant genius feature is no longer restricted to Out of combat and out of rage.

Undying Wrath

Beginning at 14th level, the beast doesn't know how to stay down, his rage lets him ignore what would normally kills anyone else. While you’re raging, having 0 hit points doesn’t knock you unconscious. You still must make death saving throws, and you suffer the normal effects of taking damage while at 0 hit points. However, if you would die due to failing death saving throws, you don’t die until your rage ends, and you die then only if you still have 0 hit points.