Amplitude

You begin to shine brightly for a few seconds, before the light fades away every creature who can see you (including allies) makes a Constitution saving throw, if failed their vision is reduced to 5ft around them.  After the light fades, various different effects take place: Your size changes to large (Do not size down), your movement speed for all acts changes to 40ft, your carrying capacity is increased to 2x its current limit, your ac increases by 1d10,  your health increases by 5d10, and you add 1d8 to all rolls.  This lasts for three rounds, at the start of your 4th turn after casting all effects are immediately removed.