The Illusory Trickster

You create a pact with a powerful patron from the Astral Sea who specializes in illusion magic, trickery and mischief. These beings are not usually strictly evil, however they are not exactly good of heart either. They thrive on illusions, creating chaos and madness in mortal realms for their entertainment. These entities generally form pacts with mortals to channel their power through, as to create chaos on realms they cannot travel to. This may be due to a limited power, or perhaps they’ve been forbidden to return to said plane. Illusory Tricksters usually communicate with their patrons via illusions that travel between planes, auditory or visual, almost as though they’ve developed schizophrenia. Only the warlock can see/hear/feel the illusions. 

Illusionist

At 1st level, you gain the ability to channel illusion specific spells through the power of your patron. This illusion magic is more powerful and harder to see through.

At will, without expending a spell slot, you can cast the spell Silent Image. Also, once per short rest, you may cast one of the following spells without expending a spell slot; Major Image, Seeming, Phantasmal Force, or Disguise self. 

The number of spells from this list you can cast without expending a spell slot starts at 1 per short rest at character level 1, then increases by one for every 4 level ups.

Trickster's Deceit

At 1st level you gain the ability to meddle with a creature's mind, making it think an illusion you created is real. When using this ability, pick a creature within 60ft of you that you can see. They must make an INT saving throw against your save DC. If the creature succeeds, the magic takes no effect and you can only try to use this ability again after a short rest. The creature also realizes the illusions are illusions, if they weren't certain before. If it fails, then the creature begins to believe any illusions around it that you have created in the past 48 hours (including disguise self, seeming, major image, or any other illusion magic) are real and act accordingly, even if they were positive the illusions weren't real before.

The spell breaks if you take damage and fail a concentration check, if the creature drops to 0 hit points, or if you choose to drop it.

Once this magic succeeds then you cannot use it again until the end of a long rest. If the creature knows you cast the illusion spell, this magic will have no effect on them. The casting time for this magic is 1 action and therefor can be used in combat.

Deception Mastery

At 6th level, you gain the ability to lie in a more convincing way. The mischievous nature of your patron is channeled through your own voice, and you are able to deceive people with more ease than before. You gain proficiency in the deception skill, and if you already had proficiency then you gain expertise. You may also add 1d8 to any ability checks involving deception, once per short rest. You may also add the 1d8 to persuasion checks, only if  the purpose of the ability check is to cause mischief in some way (e.g. convincing someone to do something that might cause chaos), or if you are trying to accomplish a task that aligns with the goals of your patron. Whether or not you can add the 1d8 to persuasion checks can be decided by the DM.

Mind's Innerworkings

At 10th level, you have mastered the art of tricking the mind and have been granted the ability to guard your own. Now understanding the innerworkings of the brain, you gain immunity to physic damage.  Also, your illusions gain the ability to mentally damage creatures in some situations. If a creature has a line of sight with an illusion you have created in the past 48 hours, and the illusion is something that would instill real fear in the creature, you can choose to force the creature to make a CHA saving throw against your save DC. If they succeed, they are no longer scared of the illusion. Should they fail, they take 2d6 physic damage and are considered frightened of the illusion, even if they know it is not real. If the DM decides that your illusion would not scare the creature, this ability is wasted. You may use this ability once per long rest, and it is an action to use. If the creature fails the save, as a bonus action you can choose to make it take another 2d6 physic damage for every subsequent round it has a line of sight with the illusion.

Mischief Maker Mastery

At 14th level, you channel all your arcane power into an illusion of your choosing, making it real. You may use your action, once per week, to turn any illusions you have made in the past 48 hours into real, material things made of matter. The construction can be an object, a creature, or a modification to a pre-existing object or creature. If the construction is an object, it crumbles to dust after 2 hours. Created objects cannot be magical in nature. If the construction is a creature, it must be a beast/monster equal to or below challenge rating 8 (and must have an intelligence score equal to or below 8), otherwise the illusion is too large or complex to transform*. The created creature uses the regular stats of whichever creature it appears to be, however it crumbles to dust if it reaches zero hit points or 2 hours have passed since transforming the illusion. If the construction is a modification to an object or creature, it reverts back to it's previous form after 2 hours, or when it is reduced to zero hit points. This also applies to any changes in landscape, such as choosing to transform an illusion created by hallucinatory terrain. 

Transforming an illusion into real matter is extremely tolling on the body. Immediately upon using this ability, you take 2d8 force damage from the arcane power being channeled through you.

*At 20th level, you can make an illusion of any creature and turn it into a real being, regardless of challenge rating. The creature can have an intelligence above an 8, though it must still be either a beast or a monster. Your DM can also choose to lower the stats of the creature you create if they decide it is too powerful.