Riptide Pilferer 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

Whenever this creature deals combat damage to a player, that player discards a card. Morph (You may cast this card face down as a 2/2 creature for . Turn it face up any time for its morph cost.)

Complete guide

Riptide Pilferer is a versatile Merfolk Rogue that uses the secrecy of the Morph mechanic to disrupt your opponent's hand. By appearing as a nameless 2/2 creature first, it can bypass early defenses before revealing its true identity to force a discard.

Understanding Morph

Riptide Pilferer features the Morph keyword, allowing you to cast it face down for {3} generic mana as a 2/2 creature with no name, creature types, or abilities. This special action does not use the stack, meaning once you decide to pay the {U} Morph cost to turn it face up, your opponent cannot respond to the transformation itself.

Triggering the Discard

The primary ability of Riptide Pilferer triggers whenever it deals combat damage to a player. For this to happen, the creature must remain unblocked. You can turn the card face up after blockers are declared but before damage is dealt to ensure the ability triggers once the damage step occurs.

Strategic Timing

To maximize the card's effectiveness, cast it face down early in the game. If your opponent chooses not to block a generic 2/2, pay {U} to flip it into Riptide Pilferer. This ensures the combat damage is dealt while the creature has its discard ability, catching your opponent off guard and stripping resources from their hand.

Common Pitfalls

Remember that turning a creature face up does not trigger 'enters the battlefield' effects, as the permanent was already on the battlefield. Also, if Riptide Pilferer is destroyed while face down, you must reveal it to all players to prove it actually had a Morph cost.

Interaction examples

The Hidden Strike

Morph

Ornithopter of Paradise

You cast Riptide Pilferer face down using the Morph reminder card. Your opponent, fearing a larger creature, blocks with Ornithopter of Paradise. Because Riptide Pilferer is blocked, it deals damage to the creature instead of the player, and the discard ability will not trigger even if you turn it face up.

Mana Efficiency

Foundry Inspector

If you have Foundry Inspector on the battlefield, it does not reduce the cost to cast Riptide Pilferer face down. Even though Morph creatures are colorless, they are not artifact spells, so you must still pay the full {3} to cast it face down.

Successful Infiltration

You attack with a face-down Riptide Pilferer. Your opponent declares no blockers. Before the damage step, you pay {U} to turn it face up. It deals 1 combat damage to the player, and the triggered ability goes on the stack, forcing that player to discard a card.

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