Subclass (5e Variant Rule)
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Subclass Variant Rule
At first level you can pick a second class. You gain the normal benefits of the class except the hit die, health and saving throw proficiency from the second class, you can only pick half the skill proficiencies (rounded down), and you level up in this subclass on every odd level of the main class. (1/1, 2/1, 3/2, so on and so forth.) Additionally, when you gain a level in the subclass which has an ability score increase, you can only use it to boost one of your ability scores by one. This is to prevent characters from becoming to overpowered while still giving them a small boost that they normally don't get.
Optional Rule: Multiclassing the subclass is not allowed, this subclass is a set of skills you picked up and slowly honed while on your journey, either learning it from a fellow adventurer or from a training manuscript. Therefore these skills can not be altered or enhanced with a secondary class.