Edgewalker — ruling 1

You apply cost reduction effects after other cost modifiers, so it can reduce additional costs or alternative costs if they include {W} and/or {B}.

Edgewalker — ruling 2

If a spell has hybrid mana symbols in its mana cost, you choose which half you will be paying before determining the total cost. If you choose to pay such a cost with {W} or {B}, Edgewalker can reduce that part of the cost.

Edgewalker — ruling 3

If you have more than one of these on the battlefield, the cost reduction is cumulative.

Edgewalker : règles, fonctionnement et interactions (MTG)

Edgewalker 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

Cleric spells you cast cost less to cast. This effect reduces only the amount of colored mana you pay. (For example, if you cast a Cleric spell with mana cost , it costs to cast.)

How it works : Edgewalker

Original English text — Wizards of the Coast / Scryfall

#1August 1, 2008· Wizards of the Coast
You apply cost reduction effects after other cost modifiers, so it can reduce additional costs or alternative costs if they include and/or .
No other card is named in this ruling.
#2August 1, 2008· Wizards of the Coast
If a spell has hybrid mana symbols in its mana cost, you choose which half you will be paying before determining the total cost. If you choose to pay such a cost with or , Edgewalker can reduce that part of the cost.
No other card is named in this ruling.
#3October 4, 2004· Wizards of the Coast
If you have more than one of these on the battlefield, the cost reduction is cumulative.
No other card is named in this ruling.