Willbender

Mana cost: {1}{U}
Type: Creature — Human Wizard
Power / toughness: 1 / 2
Set: Legions #58 (uncommon)
Price: $0.27 USD

Morph {1}{U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)
When this creature is turned face up, change the target of target spell or ability with a single target.

Willbender has 12 printings, first in Legions (2003). EDHREC ranks it #8,695 among Commander cards. It appears most in Kadena, Slinking Sorcerer decks (6,958 on EDHREC). 3 public decks on TCG run it. It has 5 official rulings.

Legality

commander: legal
legacy: legal
vintage: legal
pauper: not legal
modern: legal
pioneer: not legal
standard: not legal
brawl: not legal

Public decks that run Willbender

Enchantress Rubinia - Magic Online Theme Decks, led by Rubinia Soulsinger
Faceless Menace - Commander 2019, led by Kadena, Slinking Sorcerer
Peer Through Time - Commander 2014, led by Teferi, Temporal Archmage

Commanders that run Willbender most

Deck counts from EDHREC.

Often played with Willbender

Cards that show up in the same decks on EDHREC.

Rulings

2004-10-04: The trigger occurs when you use the Morph ability to turn the card face up, or when an effect turns it face up. It will not trigger on being revealed or on leaving the battlefield.
2013-04-15: If a spell with split second is on the stack, you can still respond by turning this creature face up and targeting that spell with the trigger. This is because split second only stops players from casting spells or activating abilities, while turning a creature face up is a special action.
2018-03-16: You don't choose the new target for the spell until Willbender's triggered ability resolves. You must change the target if possible. However, you can't change the target to an illegal target. If there are no legal targets to choose from, the target isn't changed. It doesn't matter if the original target of that spell has somehow become illegal itself.
2018-03-16: If a spell or ability targets multiple things, you can't target it with Willbender's triggered ability, even if all but one of those targets have become illegal.
2018-03-16: If a spell or ability targets the same player or object multiple times, you can't target it with Willbender's ability.