Inferno Trap — ruling 1

You may ignore a Trap's alternative cost condition and simply cast it for its normal mana cost. This is true even if its alternative cost condition has been met.

Inferno Trap — ruling 2

Casting a Trap by paying its alternative cost doesn't change its mana cost or mana value. The only difference is the cost you actually pay.

Inferno Trap — ruling 3

Effects that increase or reduce the cost to cast a Trap will apply to whichever cost you chose to pay.

Inferno Trap — ruling 4

Inferno Trap's alternative cost condition checks for any damage, not just combat damage.

Inferno Trap — ruling 5

The alternative cost condition doesn't check who controlled the creatures that dealt damage to you. Damage dealt to you by your own creatures counts.

Inferno Trap — ruling 6

The alternative cost condition is satisfied only if two different creatures dealt damage to you, not if one creature dealt damage to you twice. The damage may have been dealt to you simultaneously (as with combat damage), or at separate times.

Inferno Trap — ruling 7

You may target any creature, not just one that dealt damage to you this turn.

Inferno Trap : règles, fonctionnement et interactions (MTG)

Inferno Trap is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

If you've been dealt damage by two or more creatures this turn, you may pay rather than pay this spell's mana cost. Inferno Trap deals 4 damage to target creature.

How it works : Inferno Trap

Original English text — Wizards of the Coast / Scryfall

#1October 1, 2009· Wizards of the Coast
You may ignore a Trap's alternative cost condition and simply cast it for its normal mana cost. This is true even if its alternative cost condition has been met.
No other card is named in this ruling.
#2October 1, 2009· Wizards of the Coast
Casting a Trap by paying its alternative cost doesn't change its mana cost or mana value. The only difference is the cost you actually pay.
No other card is named in this ruling.
#3October 1, 2009· Wizards of the Coast
Effects that increase or reduce the cost to cast a Trap will apply to whichever cost you chose to pay.
No other card is named in this ruling.
#4October 1, 2009· Wizards of the Coast
Inferno Trap's alternative cost condition checks for any damage, not just combat damage.
No other card is named in this ruling.
#5October 1, 2009· Wizards of the Coast
The alternative cost condition doesn't check who controlled the creatures that dealt damage to you. Damage dealt to you by your own creatures counts.
No other card is named in this ruling.
#6October 1, 2009· Wizards of the Coast
The alternative cost condition is satisfied only if two different creatures dealt damage to you, not if one creature dealt damage to you twice. The damage may have been dealt to you simultaneously (as with combat damage), or at separate times.
No other card is named in this ruling.
#7October 1, 2009· Wizards of the Coast
You may target any creature, not just one that dealt damage to you this turn.
No other card is named in this ruling.