Colorfull tentacles

Every time the test tube is used, you have to fill it again and every time you use it, the spell will be stronger.

First time:
Squirming, light green tentacles fill a 40-foot square on 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 must succeed on a DC 2 saving throw or take 14 (2d12) bludgeoning damage and be grappled by the tentacles until the next turn. A creature that starts its turn in the area takes 14 (2d12) bludgeoning damage. 

Second time:
Yellow tentacles fill a 50-foot square on 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 must succeed on a DC 16 saving throw or take 20 (4d6 + 4) bludgeoning damage and be grappled by the tentacles until the next turn. A creature that starts its turn in the area takes 20 (4d6 + 4) bludgeoning damage. 

Third time:
Orange tentacles fill a 55-foot square on 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 must succeed on a DC 18 saving throw or take 30 (4d10 + 8)  bludgeoning damage and be grappled by the tentacles until the next turn. A creature that starts its turn in the area takes 30 (4d10 + 8)  bludgeoning damage. 

fourth time:
Red tentacles fill a 65-foot square on 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 must succeed on a DC 20 saving throw or take 35 (5d10 + 10) bludgeoning damage and be grappled by the tentacles until the next turn. A creature that starts its turn in the area takes 35 (5d10 + 10)   bludgeoning damage. 

Fifth time:
Purple tentacles fill a 80-foot square on 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 must succeed on a DC 20 saving throw or take 49 (6d12 + 10)  bludgeoning damage and be grappled by the tentacles until the next turn. A creature that starts its turn in the area takes 49 (6d12 + 10)  bludgeoning damage. 

Sixth time:
Black tentacles fill a 90-foot square on 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 must succeed on a DC 22 saving throw or take 63 (5d6+45) bludgeoning damage and be grappled by the tentacles until the next turn. A creature that starts its turn in the area takes 63 (5d6+45)  bludgeoning damage. 

Seventh time:
Huge black tentacles fill a 100-foot square on 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 must succeed on a DC 24 saving throw or take 75 (10d8+30) bludgeoning damage and be grappled by the tentacles until the next turn. A creature that starts its turn in the area takes 75 (10d8+30)  bludgeoning damage.