Domain of Tentacle

Do 1d10 roll to see how many tentacles are summoned 

Cthulhu's tentacles fill a 20-foot square on the ground that you can see within range. For the duration, these tentacles turn the ground in the area into difficult terrain.

When a creature enters the affected area for the first time on a turn or starts its turn there, the creature must succeed on a Dexterity saving throw or (number of tentacles summoned) d20 bludgeoning damage and be stunned (only have one action for the round) by the tentacles until the spell ends. A creature that starts its turn in the area and is already stunned by the tentacles takes 3d6 bludgeoning damage.

After the Tentacles is summoned, it will only stunned creatures who enter till 5 round have passed 

A creature that is stunned by the tentacles can use its action to make a Dexterity check against your spell. On a success, sent Cthulhu's tentacle back