Deal damage to Boros Reckoner
Fiendlash and Boros Reckoner trigger.
Resolve the Boros Reckoner trigger, dealing damage to any target
Resolve the Boros Reckoner trigger, dealing at least 1 damage to itself.
Repeat from step 2.

Infinite damage

Fiendlash

Boros Reckoner

Deal damage to Brash Taunter.
Brash Taunter and Fiendlash trigger.
Resolve the Brash Taunter trigger, dealing damage to an applicable target.
Resolve the Fiendlash trigger, targeting you, but dealing damage to Brash Taunter instead due to Pariah's Shield.
Repeat from step 2.

Infinite damage to target opponent

Brash Taunter

Pariah's Shield

Deal damage to the indestructible creature.
Fiendlash triggers, causing the creature to deal damage equal to the creature's power to target player or planeswalker.
Guilty Conscience triggers, dealing that much damage to the creature.
Repeat.

Guilty Conscience

Activate Pyrohemia by paying {R}, dealing 1 damage to each player and creature.
Fiendlash triggers, causing Blightsteel Colossus to give an opponent at least thirteen poison counters.
The opponent loses the game due to infect damage.
Repeat for each remaining opponent.

Combos with "Fiendlash"