Wild magic zones are geographical areas in which magic can be unpredictable. Spells cast in a wild magic zone may cause uncontrolled surges of arcane power. This applies to arcane spells, spell-like abilities, & spell completion items. If a Wild Surge occurs, roll 1d12 + 1d4. The d12 determines which metamagic effect(s) to apply. On a 4 on the d4 the GM determines an additional thematically appropriate effect (something powerful and/or strange).
The likelihood of a Wild Surge varies based on the area in question. Typically there will be an epicenter, an area of strong wild magic which becomes successively weaker over distance and eventually disappears. However, the projected effect from two or more such epicenters can interact, combining their intensity.
1: Careful: You may choose a number of creatures up to your spellcasting ability bonus. Those creatures automatically succeed on their saving throws against that spell and they take half damage if the spell doesn’t allow a save.
2: Subtle: Spell has no verbal or somatic components. Spell’s effects are invisible and silent but are otherwise unaffected.
3: Misaligned: Spell affects target(s) other than the intended one or its point of origin is a short distance from that chosen by the caster. Target(s) cannot include the caster (even for spells with a range of “personal”), but may include normally invalid ones including such things as objects or empty air if no valid target is available. A personal or touch spell will affect a target up to 30’ away. (Note: this can lead to some truly strange effects, like a fireball doing a U-turn and detonating 10’ behind you.)
4: Weak: Targets have advantage on saves; roll double the normal damage or healing dice and drop the larger half.
5: Superpowered: Targets have disadvantage on saves; roll double the normal damage or healing dice and drop the lower half.
6: Extended: Spells’ duration is doubled. Instantaneous spells create more sound than normal or generate music/noise when they otherwise would not
7: Fleeting: Duration is halved. Instantaneous spells are a strange color or create odd lighting.
8: Expanded: Double width of spell (if an area effect) or affect an additional target (if a targeted spell)
9: Efficient: Casting time decreased by 1 step. Casting time steps are bonus, standard, full-round, 10 rounds, 10 minutes, and 1 hour.
10: Difficult: Casting time increased by 1 step. Casting time steps are bonus, standard, full-round, 10 rounds, 10 minutes, 1 hour.
11: Roll twice, re-rolling 11s, 12s, and duplicates, and apply both effects. Two opposing effects cancel out.
12: Roll 3 times, re-rolling 11s, 12s, and duplicates, and apply all effects. Two opposing effects cancel out with a perceptible (but purely cosmetic) effect.