Declare a creature as an attacker. Dawnsire triggers, dealing 100 damage to the creature that has Pain for All attached.
Pain for All triggers, dealing 100 damage to each opponent.

Near-infinite damage

Pain for All

Dawnsire, Sunstar Dreadnought

Cast Pain for All by paying {2}{R}, attaching it to an indestructible creature you control with power 1 or greater.
When Pain for All enters, it triggers, causing the creature it's attached to to deal damage to another creature you control.
Howlpack Avenger triggers, dealing that much damage to the indestructible creature.
Howlpack Avenger and Pain for All trigger.
Resolve the Pain for All trigger, dealing that much damage to each opponent.
Resolve the Howlpack Avenger trigger, dealing that much damage to the indestructible creature.
Repeat from step 4.

Infinite damage

Ill-Tempered Loner // Howlpack Avenger

Cast Guilty Conscience by paying {W}, attaching it to the indestructible creature.
Cast Pain for All by paying {2}{R}, attaching it to the indestructible creature.
When Pain for All enters, it triggers, dealing damage equal to the enchanted creature's power to any target.
Guilty Conscience triggers, dealing that much damage to the creature.
Pain for All triggers, dealing that much damage to each opponent.
Repeat from step 3.

Guilty Conscience

Cast Volcano Hellion by paying {2}{R}{R}. 
When Volcano Hellion enters, it triggers, dealing an amount of damage that is less than your life total to you and the creature that has Pain for All attached.
Pain for All triggers, dealing that much damage to each opponent.

Combos with "Pain for All"