The warlock brings in to being a minor horror. <See Monster CR1 Horror - Minor>
The horror will do its best to follow the commands of the warlock. While it is in existence both share a telepathic bond. The bond is maintained as long as both remain on the same plane of existence. This bond give both the warlock and the horror advantage on saves versus Charm spells.
If the horror dies before the duration of the spell ends the Warlock may, as a reaction, spend up too 2 Hit Dice to recover hit points as though resting.
At Higher Levels:
If cast as a 4th level spell a Horror is summoned <See Monster CR3 Horror> and the Warlock gains +2 to his AC and +2 to hit with melee attacks
If cast as a 6th level spell a Grotesque Horror is summoned and the Warlock gains +2 to his AC and +2 to his melee attacks and damage
if cast as an 8th level spell an legendary Horror is summoned and the Warlock gains +2 to his AC and advantage on melee attacks and +4 to his damage
* - ((a piece of tentacle from a giant octopus or a giant squid) )