Bag of Legos

A bag of small interlocking blocks in many different shapes, sizes, and colors. Scattered these on the ground and anyone who enters the area these legos are in must succeed on a dexterity saving throw. On a failed save the target takes 1d4 piercing damage and upon entering takes an additional d4 every time they moves in the area the target also has half movement on a failed save. On a successful save the target ignores the legos completely. The legos can be scattered in an area up to 20 feet