Seeker 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

Enchant creature Enchanted creature can't be blocked except by artifact creatures and/or white creatures.

Complete guide

Seeker is a classic white Aura that provides a specific form of evasion to your most important creature. By limiting who can stand in your creature's way, it ensures your threats can bypass traditional defenses to strike your opponent directly.

What It Does

Seeker is an Aura that attaches to a creature and grants it a restrictive blocking evasion. Once enchanted, the creature can only be legally blocked by creatures that are artifacts, creatures that are white, or creatures that share both of those traits. If an opponent only controls non-artifact creatures of other colors, the enchanted creature is effectively unblockable.

How It Resolves

When you cast Seeker, you must target a creature on the battlefield. Upon resolution, Seeker enters the battlefield attached to that creature. During the Declare Blockers step of combat, the defending player checks the characteristics of their creatures; any creature that is neither white nor an artifact is prohibited from being declared as a blocker against the enchanted creature.

Common Mistakes

A common point of confusion involves multicolored creatures. As long as a creature is white, it can block the enchanted creature, even if it is also blue, black, red, or green. Additionally, colorless non-artifact creatures (such as certain Eldrazi) cannot block a creature enchanted with Seeker, as they fail both the 'white' and 'artifact' requirements.

When to Play It

Seeker is best utilized in aggressive white decks or Voltron strategies where connecting with a single large creature is the primary goal. It is particularly effective against mono-green, mono-red, or mono-blue decks that lack artifact creatures, as it renders their entire board unable to defend against your attacker.

Interaction examples

Bypassing Non-Artifact Defenses

Smothering Tithe

If you enchant a creature with Seeker while your opponent controls several Treasure tokens generated by Smothering Tithe, those Treasures are artifacts but not creatures, so they cannot block. If your opponent's only actual creatures are non-white and non-artifact, your enchanted creature will attack successfully regardless of how many Treasures they have.

Paying for the Privilege

Ghostly Prison

If you have Ghostly Prison on the battlefield and your opponent attacks you with a creature enchanted by Seeker, they must still pay {2} to attack. If they pay the cost, you can only block that creature if you control a white creature or an artifact creature. Seeker limits the defender's choices, while Ghostly Prison taxes the attacker's resources.

The Power of Equipment

Heartseeker

You can enchant a creature with Seeker and also equip it with Heartseeker. The creature will gain +2/+1 and the ability to destroy a target creature. Because of Seeker, your opponent will likely be unable to block it. If they do happen to have a white or artifact creature that can block, you can use the Heartseeker ability to destroy that specific blocker before damage is dealt.

Guide written with AI from the official text and rulings. Official English text prevails.

How it works : Seeker

Original English text — Wizards of the Coast / Scryfall

No additional ruling has been published for this card.

Interactions with other cards

These cards' text mentions Seeker.

Heartseeker

Equipped creature gets +2/+1 and has "{T}, Unattach Heartseeker: Destroy target creature." Equip {5} ({5}: Attach to target creature you control. Equip only as a sorcery.)