Though many spellcasters like to consider their use of magic a science, the effects of magic are not always easy to predict. Wild, uncontrolled magic sometimes surges as a side effect of spellcasting or magical experimentation. Wild magic can be used in any situation where magic might cause randomness and chaotic effects. When a character casts a spell or takes an action that could trigger a surge of wild magic (see Implementing Wild Magic below), roll on Table: Wild Magic Surge.
Roll to determine the surge effect before the spell is cast, but apply the effect after the spell is cast unless it alters the spell itself in some way (such as changing the effective caster level). Any reference on the table to the spell or the spell’s level applies to the spell being cast, supernatural ability being used, or magic item effect being activated. Similarly, any reference to the caster applies to the character who triggers the surge. If an effect requires a caster level, use the caster’s full character level.
If the wild magic surge effect you roll isn’t possible due to the nature of the spell or effect, roll instead on Table: Universal Surge Effects. A wild magic surge effect doesn’t allow a saving throw, even if it’s replicating a spell that normally would, and any effect that would normally have a limit on the amount of Hit Dice it can affect ignores that limit. Higher results on the table are more likely to be beneficial, so a GM might give a bonus or penalty on the check if an action would alter how likely it is that the wild magic surge would be helpful.
Though the rules on when to use wild magic are deliberately vague to give the GM leeway, here are some suggestions, presented in order from simplest to most complex.
Failed Concentration: When a caster fails a concentration check, and thereby loses a spell, some of the spell’s energy escapes in a wild magic surge.
Dispel and Counterspell: When a spell or magical effect is dispelled or counterspelled, it triggers a wild magic surge on the caster or subject.
Wild Zones: Some places are magically unstable. When a creature casts a spell, uses a spell-like ability, or activates a magic item in such an area, it causes a wild magic surge.
Boost Casting: A caster can attempt to use a metamagic feat she has with a spell she’s casting without expending a higher-level spell slot, needing to prepare the spell at a higher level (if a prepared caster), or increasing the casting time (if a spontaneous caster). To do so, she must attempt a caster level check with a DC equal to 10 + the spell’s level + 5 for every increase in spell level the metamagic feat would normally cause. If she succeeds, her spell gains the metamagic feat’s benefit and she causes a wild magic surge. If she fails, she still rolls on Table: Wild Magic Surge, but subtracts from the result a number equal to the amount by which she failed the check.
Pathfinder Roleplaying Game Pathfinder Unchained © 2015, Paizo Inc.; Authors: Dennis Baker, Jesse Benner, Ross Beyers, Logan Bonner, Jason Bulmahn, Robert Emerson, Tim Hitchcock, Jason Nelson, Tom Phillips, Stephen Radney-MacFarland, Thomas M. Reid, Robert Schwalb, Mark Seifter, and Russ Taylor.