Wild Magic is the unexpected effect that happens when someone below fifth level casts a spell. The scribes and scholar of Pelbon have come to understand that this happen due to the individals inability to contain the Primal Energy that is used to cast the spell. The effect lessens as the spell caster gains experience this is offset by the level of the spell being cast.
Level of CasterBase Chance of Wild Magic Effect
140%
230%
320%
410%
55%
Level of SpellBase Chance of Wild Magic Effect
12%
24%
36%
48%
510%
612%
714%
816%
918%

Wild Magic effects will also happen to anyone within 150' of an active Gothaem Storm or in the area within two hours of its passing (this is regardles of the size of the storm). The chance of a Wild Magic effect is 60% base plus any modifiers indentified above, This effect does diminishes by 15% every 30 minutes regardless of the spell casters level.

A few examples: Milifanse a 2nd mage is going to cast Faerie Fire, a 1st level spell, so there is a 32% chance of a Wild Magic effect occuring. Should Milifance casts the same spell as a 6th level mage, there would only be a 2% chance of Wild Magic. If he were to cast this spell right after a Gothaem Storm, the chance would be 62%

With regards to clerical spells and the calling down of divine retribution or aid, if the priest has not performed the required prayers and/or sacrifices for that days spell, they will receive none. There is however, a standing 2% chance each (non cumulative) day that if a priest calls down the name a specific deity (Demi or above in status) they will answer. This does not guarantee a positive or negative response, the deity actually showing up in person, or the priest not being struck down where they stand. Be rest asured they will answer in some form or fashion

World Codex