Doom Hound

Prerequisite: 7th level, Pact of the Chain Invocation, Hunter in Darkness patron

As a bonus action, your familiar transforms into a more powerful creature for 1 minute. At 7th level and higher, it transforms into a dire wolf. At 12th level and higher, it transforms into a winter wolf. At 18th level and higher, it transforms into a hound of the night. You must finish a short or long rest before you can use this invocation on your familiar again.