Pact of the Helm

It is said that when the spheres were young, two great creations were forged at the same time: The Spelljammer and The First Helm. While The Spelljammer is the first and oldest of all ships that sail the rainbow sea, the First Helm is the artifact from which all spelljammer Helms are born. Each spelljammer Helm is connected to the First Helm, constantly sending information back to it from the mind of an attuned Helmsman. The stories say that the First Helm is gathering knowledge for some unspeakable horror to come. Reasonable people recognize these stories as tall tales. Reasonable people know that countless wizards have investigated that although they can't replicate spelljammer Helms, there is no sign at all of information being extracted from a Helmsman. Reasonable people don't put much stock in silly, unsubstantiated rumors told by sailors with too much time on their hands. Reasonable people are wrong. You know that the First Helm is real. You know that the First Helm has had its hand in the mind of every single spellcaster who has ever attuned to a spelljammer Helm. You have glimpsed the depths of the knowledge it has accrued and recognized that it may know more than even the gods. You don’t know what exactly the First Helm seeks or what it values, whether it is benevolent or malevolent, you only know just how much knowledge it has gathered… 

At this point, the only reasonable thing to do is join it. 

Expanded Spell List

1st-level Pact of the Helm feature

The Pact of the Helm lets you choose from an expanded list of spells when you learn a warlock spell. The Pact of the Helm Spells table shows the spells that are added to the warlock spell list for you

Level

1. catapult, bane
2. mind thrust, nystul's magic aura
3. stable gravity, intellect fortress
4. enhance/reduce maneuverability, confusion
5. modify memory, rary's telepathic bond

Attuned Mind

Starting at 1st level, the influence of the First Helm has granted you unique knowledge of spelljammers. You gain tool proficiency with air vehicles. In addition, while attuned to a spelljammer Helm, you can telepathically speak to any creature within your spelljammer's air envelope. You don't need to share a language with the creature for it to understand your telepathic utterances, but the creature must be able to understand at least one language.

Mental Adaptability

Starting at 6th level, you gain resistance to psychic damage, and you have advantage on saving throws against being charmed or frightened. In addition, as a bonus action on your turn, you can temporarily learn a spell from the Warlock spell list that you don't already know. For the next minute, you can cast this spell as if it was one of your known spells. Once you use this ability, you can't do so again until you finish a long rest.

Infinite Knowledge

Starting at 10th level, as an action you can call upon the power of the First Helm to spontaneously cast a spell you don't know from the Wizard, Sorcerer, or Artificer spell list without expending a spell slot. This spell must have a casting time of 1 action and must be 5th-level or lower. You still need to provide spell components with a gold cost and perform verbal and/or somatic components when casting the spell. After you use this ability, you can't do so again until you finish a long rest. In addition, your Mystic Arcanum class features count as spell slots for helmsman spell abilities.

Pefectly Attuned Mind

Starting at 14th level, when you attune to a spelljammer Helm, you are no longer rendered helpless. So long as you remain within the air envelope of your spelljammer, you can continue to control the spelljammer as if you were sitting on the Helm. During combat, you can act both as a Helmsman in spelljammer combat and using your character abilities against boarding parties in ground combat.