Skill specialist

You have trained to become an expert in a specific skill. Now you almost never fail when you use this skill, and when you succeed you do so spectacularly. Choose one skill that you already have proficiency in, you gain the following benefits based on that skill. 

• Increase the ability score related to the skill you chose by one 
• you gain expertise in that skill 
• if you need to use an action or bonus action to make a check related to that skill you can instead do it as a free action 
• if you roll a natural 1 on a skill check for this skill you can roll again and use the new roll 
• if you roll a natural 20 on a skill check for this skill you gain a specialist token which you can use to give an ally advantage on a check for this skill. You loose all specialist tokens when you take a long rest.