Deal damage to Boros Reckoner
Donna Noble and Boros Reckoner trigger.
Resolve the Donna Noble trigger, dealing that much damage to an opponent.
Resolve the Boros Reckoner trigger, dealing that much damage to itself.
Repeat from step 2.

Infinite damage

Donna Noble

Boros Reckoner

Deal damage to Donna Noble or the creature it is paired with.
Donna Noble and Blazing Sunsteel trigger.
Resolve the Donna Noble trigger, dealing damage to an opponent.
Resolve the Blazing Sunsteel trigger, dealing damage to the creature it is attached to
Repeat from step 2.

Blazing Sunsteel

Deal damage to Donna Noble.
Donna Noble triggers, dealing damage to an opponent.
Guilty Conscience triggers, dealing damage to Donna Noble.
Repeat from step 2.

Infinite damage to target opponent

Guilty Conscience

Deal damage to Donna Noble.
Donna Noble and Fiendlash trigger.
Resolve the Donna Noble trigger, dealing damage to an applicable target.
Resolve the Fiendlash trigger, targeting you, but dealing damage to Donna Noble instead due to Pariah.
Repeat from step 2.

Fiendlash

Pariah

Declare any creature as an attacker. Dawnsire triggers, dealing 100 damage to  Donna Noble.
Donna Noble triggers, dealing 100 damage to target opponent.

Near-infinite damage to target opponent

Dawnsire, Sunstar Dreadnought

Deal damage to Donna Noble.
Donna Noble and Repercussion trigger.
Resolve the Donna Noble trigger, dealing damage to an applicable target.
Resolve the Repercussion trigger, dealing damage to Donna Noble instead of you due to Pariah.
Repeat from step 2.

Repercussion

Cast Volcano Hellion by paying {2}{R}{R}.
When Volcano Hellion enters, it triggers, dealing an arbitarily large amount of damage to you and a creature. The damage that would be dealt to you is dealt to Donna Noble instead due to Pariah.
Donna Noble triggers, dealing an arbitrarily large amount of damage to an applicable target.

Volcano Hellion

Cast Wheel of Misfortune by paying {2}{R}, choosing an arbitrarily large number and having Wheel of Misfortune deal that much damage to Donna Noble instead of you due to Pariah if you chose the largest number.
Donna Noble triggers, dealing that much damage to an applicable target.

Wheel of Misfortune

Earthbend a basic land you control.
Cast Legolas's Quick Reflexes by paying {G}, targeting the earthbent land.
Activate Earthcraft by tapping the earthbent land, targeting the earthbent land.
The land triggers, causing it to deal damage equal to its power to Donna Noble.
Donna Noble triggers, dealing that much damage to an applicable target.
Resolve the Earthcraft trigger, untapping the earthbent land.
Repeat from step 3.

Combos with "Donna Noble"