When a spell is cast within range you use your understanding of the magical weave to tamper with its arcane structure. If the spell is 5th level or lower roll a d6.
On a 1-2: The intensity of the spell is halved. If the spell deals damage, the damage is halved. Any other effects have their duration halved and any additional saving throws against the spell have advantage.
On a 3-4: The intensity of the spell is halved as above. In addition the casters ability to aim the spell is broken. The spell now targets a random creature within range (excluding the caster and intended target). In the case of area of effect spells the spell is now centred on a random creature in range. If there are multiple targets of the spell each target is randomized.
On a 5-6: The fracturing nature of the spell has reached its peak and the magical constraints of the spell fail causing a magical detonation dealing 4d12 force damage (or a suitable elemental type at the DMs discretion) in a 10ft radius of the creature taht cast the spell

If the target spell is 6th level or above make an ability check using your spell casting ability modifier. The DC is 10 + the spells level.

At Higher levels: When this spell is cast using a spell slot of 6th level or above, the target spell is fracture without a roll if its level is less than or equal to the level of the spell slot you used. In addition the damage dealt by a magical detonation increases by 1d12 for every level above 5th.