Inferno Titan

{R}: This creature gets +1/+0 until end of turn.
Whenever this creature enters or attacks, it deals 3 damage divided as you choose among one, two, or three targets.

Bloomburrow Commander

{R}: Inferno Titan gets +1/+0 until end of turn.
Whenever Inferno Titan enters or attacks, it deals 3 damage divided as you choose among one, two, or three targets.

Commander Masters

{R}: Inferno Titan gets +1/+0 until end of turn.
Whenever Inferno Titan enters the battlefield or attacks, it deals 3 damage divided as you choose among one, two, or three targets.

Historic Anthology 7

"I daresay there's more truth in some of them stories than you reckon."
—Sam

Tales of Middle-earth Commander

You divide the damage as you put Inferno Titan's triggered ability on the stack, not as it resolves. Each target must be assigned at least 1 damage. (In other words, as you put the ability on the stack, you choose whether to have it deal 3 damage to a single target, 2 damage to one target and 1 damage to another target, or 1 damage to each of three targets.)