Slay the Spire inspired subclass for the Ironclad!

Level 3: Flex

When you choose this subclass at level 3, your strength begins to empower your rage! When you go into a rage you gain 1 Strength. For each Strength you gain, it adds +1 to your STR score. You can only gain Strength during a rage, your strength ends at the same time your rage does. In addition, you can use a bonus action on each of your turns to gain one Strength. This can be used up to a number of times equal to your proficiency bonus per short rest.

Level 6: Thunderclap

At level 6, your strength is so overpowering it begins to effect your enemies! When you attack an enemy during a rage, using a reckless attack, you can choose a damage type you attacked with and force the enemy to make a (DC 10 + prof bonus + STR score) CON saving throw or be vulnerable to it until the end of your turn. This can only be done to one enemy at a time. You can use this ability up to a number of times equal to your proficiency bonus per short rest.

Level 10: Demon Form

 At level 10, your strength becomes overbearing, an eminence forms around you. You can take an action to enter Demon Form, this form allows your Strength to stack. When in Demon Form, and in a rage, at the beginning of each of your turns you gain 2 Strength. 

Level 14: Limit Break

 At level 14, your Strength no longer knows any bounds. You can now gain Strength while you are not raging. There is no longer a limit to how many enemies are effected by Thunderclap, or how many charges of Thunderclap or Flex you have. No limits baby! You can use this ability up to 2 times per Long Rest. When you have no charges remaining of Limit Break, you can instead expend 1 Rage to enter Limit Break.