Someone can bond to you as their weapon.  The person can use their bonus action to turn you into your weapon form if wielding you and you are willing. (if you are unwilling you make a Wisdom save, the DC equals 10 + their wis mod). If you roll before your wielder in battle, you must use your action to "Help" - and give your bonus action to your wielder, who then then transform you. You can partially transform yourself.  You can turn your arms or legs into your weapon form without fully turning yourself into a weapon. Doing so gives you disadvantage on attack rolls. It requires concentration to fight this way.  If you partially transform into a weapon that is two-handed, the damage die goes down one size (2d6 > 1d12 > 1d10 > 1d8 > 1d6). 

You can cast Shield a number of times equal to ½ your proficiency bonus per long rest.  In addition you can cast it on an ally within 30ft as a reaction when they are hit.

You can, as a bonus action, spend a hit die to deal extra psychic damage when you make a successful attack.  The extra damage is calculated as two times hit die spent. You cannot spend more than two hit die at a time when you do this. Example, you make a successful weapon attack with a shortsword, doing 1d6 + str or dex mod damage.  You then use your reaction, and spend 1 hit die to deal extra damage; the extra damage is equal to 2d8.

Lastly, when the person you are bonded to is hit, you can use your reaction to dash to their side (if in movement range), and take the hit for them.  If your AC is higher than the triggering attack, it misses, otherwise you take the damage.