As a Magic action, you can flatten your body into a shadow upon the floor. You remain in Umbral Form until you end this effect as a Bonus Action. While in Umbral Form, the following rules apply.
Inactive
You can't take any action, Bonus Action, or Reaction, other than to leave the form.
Immunities
Difficult Target
Attacks against you have Disadvantage.
Invisible in Darkness
While entirely in Darkness, you have the Invisible condition to any creature that relies on Darkvision to see you in that Darkness.
Speed
Your Speed doubles and you gain a Climb Speed equal to your Speed. You can move across difficult surfaces, including ceilings, without needing to make an ability check. As a shadow, you can only move along surfaces; you can't jump or fly.
Gear
Your equipment merges with your Umbral Form and has no effect until you leave the form.