ReRolls and Unmodified effects

[LeSwordfish]

Hexgorger Skulls cause spellcasting attempts near them to fail on an unmodified roll of an 8, and further bad things then happen. Successful spellcasting rolls near a Bloodsecrator must be re-rolled. If my opponent is near both and rolls a successful 8, does it fail or get re-rolled?

[T10]

According to the Designers Commentary on re-rolls, modifiers and successful/failed rolls, if a re-roll is dependent on a success/fail condition, the actual roll is compared to the required value do decide if the re-roll is warranted.

For example, if an attack has a To Hit of 4+ and a rule states that failed  hit rolls  must be re-rolled, then if the dice roll is 1, 2 or 3 then it must be re-rolled even if modifiers would make the roll succeed. A combination of a +1to hit and this rule can conspire to turn a "good" roll bad: You roll a 3, which is going to be a hit with the modifier, but you are forced to re-roll.

Back to your issue.

You roll an 8 and re-rolls are considered. Looking only at the casting value required, this is a success and must be re-rolled due to the Bloodsecrator. If you roll an 8 again the casting roll succeeds compared to the casting value, and this is overridden by the Hexgorger Skulls and hilarities ensue.

-T10