Needlebite 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.

Needlebite 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.

Needlebite Trap — ruling 3

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

Needlebite Trap — ruling 4

Needlebite Trap's alternative cost condition checks only whether life was gained. It doesn't care whether life was also lost. For example, if an opponent gained 4 life and lost 6 life during the turn, that player will have a lower life total than they started the turn with — but you can still cast Needlebite Trap by paying {B}.

Needlebite Trap : règles, fonctionnement et interactions (MTG)

Needlebite 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 an opponent gained life this turn, you may pay rather than pay this spell's mana cost. Target player loses 5 life and you gain 5 life.

How it works : Needlebite 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
Needlebite Trap's alternative cost condition checks only whether life was gained. It doesn't care whether life was also lost. For example, if an opponent gained 4 life and lost 6 life during the turn, that player will have a lower life total than they started the turn with — but you can still cast Needlebite Trap by paying .
No other card is named in this ruling.