Weird magic is weird and you can now do it for fun nonsensical effects designed specifically to make the DM go insane.

Bizarre Spells

Beginning when you select this school at 2nd level, you may spend your downtime and gold to modify a spell in your spellbook. It cost 1 day of downtime and 10 gold for every level of the spell you modify. If you do so it gains an additional effect determined by its school.

Abjuration: You may choose to have the target's speed reduced by 10ft or you may take damage equal to the level of the spell to give a target 1d8 temporary hit points (maximum of the spell's level)

Conjouration: You may choose to create take damage equal to 1d12 + twice the spell's level and cast increase the spell's duration or effect by 50%

Divination: You gain a piece of information about the targets deepest nightmares and worst fears. Higher level spells give more detailed information

Enchantment: You may cause the target to fear you for rounds equal to the spell's level

Evocation: You may take damage up to twice the level of the spell and cause the spell to deal extra damage equal to the amount taken - 1d4 (minimum of 1)

Illusion: You may make any illusion bizarre and scary. The target must make a Wisdom save or be incapacitated for turns equal to half the spells level rounded up.

Necromancy: You may cause your flesh to appear rot for a number of turns equal to the spell's level. For the durration, you gain advantage on intimidation and melee weapon attacks made by you deal an extra 1d4 poison damage

Transmutation: Whenever you modify or create a material you can choose for the material to be more macabre, without affecting the mechanical effects (Such as Create/Destroy water creating blood, Giant Insect creating an insectoid horror, Spike Growth creating spikes made of bone, etc.) OR you may cause the target of the spell to change their appearance (into a macabre deformation of their original form) for the spell's duration, during the appearance change they gain disadvantage on Charisma but can add half your Intelligence modifier (rounded up) to the damage of attacks they make.

Macabre Potions

Beginning at 2nd level, you gain proficiency in Alchemist's Supplies if you didn't already have it. Also beginning at 2nd level, you may spend your rest to create a macabre potion. Doing so takes no gold but requires Alchemist's Supplies. If you spend a short rest it heals 1d4 hp and if you spend a long rest it heals 1d6 hp. When the potion is used it has an additional effect determined by how much hp it healed. The potion looks like blood, smells like rotten flesh, and tastes like spoiled milk.

1. The drinker gains temporary hit points equal to your Intelligence
2. The drinker has disadvantage on concentration checks for 24 hours
3. The drinker becomes nauseous for 1d4 hours. For the duration of nausea, they have disadvantage on Constitution
4. The drinker believes that they are you for the next 10 hours. They act like you the best they can and are completely okay with the fact that there are two of you. They can't be swayed to think otherwise
5. For the next 2d12 hours the drinker gains inspiration every time they take more than double their Constitution modifier worth of damage
6. The drinker heals another d6 of hp and rolls again for another effect

Weird Magic Items

You can spend a spell slot and 1d12 days of downtime to make a weird magic item. The item has an effect similar to a Bizzare spell you know and can cast but the item has a cumulative 5% chance of backfiring in a way determined by the DM every use (chance increase to 10% if the spell is over level 5, and to 30% if the spell is over level 8). You could also choose an item from below which have a non-cumulative 5% chance of backfiring. 

• Potion of Bees (Potion): You may use an action to either throw or uncork the potion. If you do so a swarm of wasps flies out of the potion and attacks whoever is closest. The swarm leaves after 1d8 turns without taking damage or having anyone pass through the swarm.
• Bracer of the Beast (Wondrous Item, requires attunement): While wearing this studded hide bracer, you can use a bonus action to speak its command word, transforming your hand into a giant crab's claw. While transformed, your unarmed strike deals 1d6 bludgeoning damage and the target is grappled. The effect lasts until you speak the command word again, which causes your hand to revert to its normal form.
• Oil of Rotting Flesh (Potion): This rancid oil can cover a Medium or smaller undead skeleton, and takes 10 minutes to apply. The affected undead is transformed into an undead zombie.
• Prismatic Blade (Weapon, longsword, requires attunement): This item appears to be a longsword hilt. While holding the object, you can use a bonus action to cause a blade of prismatic radiance to spring into existence, or make the blade disappear. While the blade exists, this magic longsword has the finesse property. When you hit a target with this weapon, roll 1d6: 1. the weapon deals fire damage, 2. acid, 3. lightning, 4. poison, 5. cold, 6. no damage but the target is blinded until the start of your next turn.
• Bone Figure (Wondrous Item): This bone statute can take on the form of any creature as long as it soaks in that creature's blood for 1d4 hours. If it does this the stature loses any previous forms it had and gives an advantage on any attack made towards the creature whose form it has.
• Amulet of Weird Luck (Wondrous Item, Requires Attunement): Whenever you roll a die while attuned to this item, instead flip a coin: If heads you roll a 1 if tails you roll whatever number is highest.
• Scroll of Gibberish (Scroll): Whoever reads the scroll needs to make a Wisdom saving throw or gain an indefinite madness of your choice. The Scroll is destroyed after use.

Eldritch Arcana

Beginning at 10th level, you learn the eldritch blast cantrip. You also learn a number of warlock spells equal to your Intelligence Modifier. You add them to your spellbook as Bizarre spells. The warlock spells' level can't be greater than level 3.

Weird World

Starting at 14th level, you gain the ability to create a nightmarish pocket dimension that only you can navigate. You can spend 1 minute concentrating to open a portal to or from the pocket dimension. The portal lasts for 1d4 minutes but can be dismissed by you as a bonus action. You control all of the reality inside the pocket dimension, however, things from inside the pocket dimension can't be removed. Anyone trapped for more than three days in the pocket dimension has to make a Wisdom saving throw or gain an indefinite madness. If they succeed they have to re-roll every 24 hours with a cumulative -1 every time.