You reach into the weaves of the underlying tapestry of raw magic.  The weave becomes tangled, causing strange side effects whenever someone tries to utilize it in spellcasting.  Choose a point within range.  A 30-ft. sphere originating from that point becomes a wild magic zone.  Whenever a creature casts a spell in that area, roll a d8, and consult the table below:

1 - 2 :  The spell fails.  Roll on the Wild Magic Surge table in the Player's Handbook.  

3 - 4 :  The spell casts:  Roll on the Wild Magic Surge table in the Player's Handbook.  

5 :  If the spell requires an attack roll, roll it with advantage.  If the spell requires a saving throw, creatures affected by the spell roll with disadvantage.  

6 :  If the spell requires an attack roll, roll it with disadvantage.  If the spell requires a saving throw, creatures affected by the spell roll with advantage.  

7 :  A surge of magical energy erupts from the caster, causing it to take (2d8) force damage.  Any creatures within 5 ft. of the caster must succeed on a Dexterity saving throw or take (1d8) force damage.

8 :  All creatures within the wild magic zone must roll 1d12;  If the roll is even, a creature gains an amount of temporary hit points equal to the number rolled.  If the roll is odd, a creature takes an amount of necrotic damage equal to the number rolled.  

At Higher Levels.  When you cast this spell using a 4th-level spell slot or higher, the radius of the wild magic zone increases by 10 ft. for every two spell slot levels above 2nd.  Additionally, the force damage, necrotic damage, and temporary hit points each gain one extra die for each spell slot level above 2nd.