The Envy Pact
Your patron is unknowable dark spirits which are the actual overlords of the plane of Envy. This plane attracts those that want what others have, but do not have the drive to actually go out and earn what they want. Other sins have things about them that help those attracted to them (Gluttony = being well fed, Sloth = well rested, Greed= prosperity, etc.) but Envy just makes those that seek its charms bitter. Warlocks of Greed and Envy are often each others enemies like no two other combinations of Synn warlocks are, as one wants to keep everything and the other covets everything.
Expanded Spell List
Like other warlock pacts, you have an expanded spell list, reflecting the envious nature of your powers.
3rd Bestow Curse
Envy Warlocks can’t help but want what others have. At 1st level the Envy Warlock has the ability to observe any spell he sees someone else cast and add it to his expanded spell list. He can only have two spells for each level gained this way, and can not change them out until he gains a level.
Like other pacts, you gain your choice of a pact boon at 3rd level. If you choose Pact of the Chain, your familiar will usually be the best looking familiar you ever saw someone have. If you choose Pact of the Blade, your weapon will usually look like the most impressive weapon you have ever seen. If you choose Pact of the Tome your tome will usually look like a the most impressive book you ever seen. This ability could mean the item gained looks like an artifact, but it would not have the same abilities…only look the same.
The Synn Planes know their own, and Envy Warlocks are no exception. Starting at 6th level, you may travel at any time to the Plane of Envy. This will usually take a minute unless 1) you are already on one of the other Synn Planes or 2) you have driven yourself nuts seeing people better off than you, in which case you will plane walk within seconds. After a short rest you can travel back to the plane you came from. Traveling once again to the Envy plane in this manner requires a long rest unless you are on another of the Synn planes, which then only requires a short rest.
Everyone wants what Everyone else has.
The plane of envy wants as many denizens as possible. At 10th level you may teleport Xd4 hit dice of humanoids to the plane where X equals your current warlock level. Those teleported will usually imagine seeing people have everything they themselves have always wanted. Intelligent creatures who do not wish to be teleported must save against your spell save DC, using their wisdom; if they are miserly they have disadvantage. Those disappointed in not getting what they wanted will often be easily persuaded to become envy warlocks…another reason envy warlocks are the most numerous of the Synn Plane warlocks even thro they are the most unhappy.
Every one in a while it is a boon to covet. At 14th level the Envy Warlock gains the ability to copy any other warlock pact power he has seen and perform it as well. While he may copy many powers, they will only be half as effective, and he will never really understand how come they are not as powerful as what he’s seen others do. If the original warlock power specifically wrapped itself around a Synn Plane, the new power for the Envy Pact becomes wrapped around Envy.