Ultra Instinct is a form you can gain access to by buying the skill from Whis in Kami's lookout, or Jin on King Kai’s planet in Other World. It costs 500,000 TP and 10 Mind. It has 3 levels, with upgrade 1 costing 200,000 TP(100,000) and 15 Mind, and upgrade 2 costing 300,000 TP and 20 Mind(configurable). You must also have the skill God Form to use Ultra Instinct, which can be acquired by the same NPCs. Saiyans require God Form to be level 2.
The ability to use Ultra Instinct can be toggled in the Action Menu, is activated with the Bloodline Power On (aka Transform) hotkey, and will not activate if you’re already in a transformed state(Super Saiyan, Ozaru, God Form, ect). You can only transform when below 30% health.
There are 3 stages to Ultra Instinct that each activate depending on how much you’ve upgraded the skill. Stage 1 is Ultra Instinct Sign, with a 3x stat increase. Stage 2 is near perfection, with a 3.5x stat increase. Stage 3 is Mastered Ultra Instinct, with a 4x stat increase. To gain access to Mastered Ultra Instinct, you must also experience Pain, a debuff you are inflicted with when in Ultra Instinct for too long. All stages also give an increasingly higher chance to dodge attacks. and change some things... first stage lowers health by 1hp per second and cant heal above the 30% second stage nullifies that (the healing above thing is increased a bit to 50% i believe) and third stage attacks back when dodging automatically can heal higher than stage 2