Mechanically, when the target of a Fatespinner's spell passes their saving throw, they are forced to reroll that saving throw. The second result stands, pass or fail.
1 - Allow reroll of saves on 1st - 3rd Level Spells
2 - Allow reroll of saves on 4th - 6th Level Spells, +1 DC to all spells, +1 caster level, +10% increased caps.
3 - Allow reroll of saves on 7th - 9th Level Spells, +2 DC to all spells, +2 caster levels, +20% increased caps.
The rerolled save receive an additional bonus of 1 point of DC per rank of Spell Focus: Divination (ie, +3 for Epic Spell Focus: Divination).
The bonuses to DCs, caster levels and spell caps apply to all spells, not just Divinations.