Dr. Flumph's Potted Plant

You place the potted plant on the ground in front of you, and the plant immediately grows to Large (and the pot grows to accommodate) and three of the flowers or leaves grow into mouths with sharp, pointy teeth (specific aesthetics depend on the potted plant). You can order the plant to guard an object, person, doorway, or passage. It recognizes you as its creator and won’t attack you, and up to ten creatures of your choice. Any other creature that attempts to pass without speaking the password written on the inside of the pot is subject to attack. The plant has +5 to initiative, and on its turn, it makes three melee attacks (range 5 ft., + the level of the spell slot you used to hit), one with each head. On a hit, the target takes 3d6 piercing damage, and if the target is medium or smaller, the plant can have the target make a Strength or Dexterity saving throw (target’s choice) with your spell save DC. On a failed save, the target is swallowed, is restrained, and at the beginning of the target’s turn it receives 8d6 acid damage. A swallowed creature can attempt to escape by making a Dexterity or Strength saving throw (the target’s choice) as a bonus action on its turn (DC is your Spell save), freeing itself on a success. The plant can swallow one creature per head. If you cast this on the plant 24 hours in a row, the plant gains 50 hit points and 15 AC and will guard what you designated until it is destroyed.

At Higher Levels. When you cast this spell using a spell slot of 6th level or higher, the plant gains an extra mouth (meaning one additional attack/swallowed creature) for each spell slot above 5th. The duration also increases by 1 hour for each spell level above 5th.