Ason's Falling Floor

You craft an illusion that takes root in the mind of a creature that you can see within range. The target must succeed on a Wisdom saving throw. On a failed save the creature becomes convinced that the floor beneath its feet is always crumbling away.

• The creature must use all of its base movement speed on each of its turns for the duration. The creature must move in a straight line until it comes to an obstacle or runs out of movement.
• If it collides with an obstacle before it runs out of movement it must turn 90 degrees and continue in a straight line as before.
• The creature cannot willingly move back onto any ground that it has previously occupied this turn.
• If the creature is forced to move through or end its movement on a position that it has already occupied this turn, the target must succeed on a Dexterity saving throw, or be knocked prone ending the spell. On a success, the illusion is revealed and the spell ends.
• While under the effect of this spell, movement does not leave the target open to attacks of opportunity. 

The creature can use actions as normal on each of its turns as long as it follows the movement rules above. On each of its turns the creature may choose to use its action to make an investigation check against your spell save DC. On a success, the creature discovers the illusion and the spell ends, on a fail, the illusion continues.

(credit to THum05 for the original version)