Clockwork Heart

The clockwork heart counts as a magical item and is under the same rules as a magic item would normally be, except it does not require attunement and is for all intents and purposes embedded and bound to the character. By surging infused magical power through the players body, the heart increases the capabilities of the characters body.

The heart allows the carrier to add 1d4 to any strength or dexterity based ability or skill check or saving throw once per long rest. Alternatively in combat the heart enables one dash, charge or extra attack as a bonus action once per long rest. Any one use of this heart counts as the heart being used until the next long rest. The heart comes with a winding key and a slot for it in the characters chest. The heart must be rewound every long rest and failing to do so at least once per every day will increase the players exhaustion level by one per every day if it's not rewound. The key is non-magical and of simple make, easily replaceable by any blacksmith.