Kelpie Guide 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

: Untap another target permanent you control. : Tap target permanent. Activate only if you control eight or more lands.

Complete guide

Kelpie Guide is a versatile blue creature that offers utility in the early game and control in the late game. By manipulating the state of other permanents, it ensures your strategy stays fluid while your opponents find their plans stalled. As a Beast that interacts with your land count, it bridges the gap between mana ramp and tactical dominance.

Dual Utility on the Battlefield

Kelpie Guide possesses two distinct activated abilities, both requiring it to tap. The first ability allows you to untap another target permanent you control, which can be used to reuse mana-producing lands, reset artifacts, or give a creature pseudo-vigilance. The second ability, which becomes available only when you control eight or more lands, allows you to tap any target permanent, effectively neutralizing an opponent's biggest threat or tapping down a blocker before your combat phase.

Understanding the Land Requirement

The second ability of Kelpie Guide has a restrictive activation requirement. You must control eight or more lands to even put the ability on the stack. However, if the number of lands you control drops below eight after the ability has been activated but before it resolves, the ability will still resolve normally. Note that the first ability specifically targets 'another' permanent you control, meaning Kelpie Guide cannot untap itself.

Strategic Timing and Placement

Because Kelpie Guide must tap to use its abilities, haste is highly beneficial if you wish to use it the turn it enters. In the early game, use it to untap lands that enter the battlefield tapped to stay on curve. Once you hit the late-game threshold of eight lands, Kelpie Guide transforms into a defensive piece, allowing you to tap down an opponent's creature at the end of their beginning of combat step to prevent them from attacking.

Interaction examples

Speeding Up Resource Growth

Solemn Simulacrum

You cast Solemn Simulacrum and search for a basic land, putting it onto the battlefield tapped. While that land would usually be unusable until your next turn, you can activate Kelpie Guide to untap that specific land immediately, giving you access to one more mana during your current turn.

Navigating Ability Restrictions

Roaming Throne

If you name 'Beast' with Roaming Throne, it is important to note that Roaming Throne only doubles triggered abilities. Since Kelpie Guide features activated abilities (denoted by the 'Cost : Effect' format), Roaming Throne will not cause Kelpie Guide to untap or tap an additional permanent. You will still only get one use of Kelpie Guide's tap ability per turn cycle unless you have a way to untap the Guide itself.

Late Game Lockdown

Once you have eight lands in play, you can use Kelpie Guide during your opponent's upkeep. By tapping their only source of a specific color of mana or their largest creature, you dictate the flow of their turn. Because the second ability can target 'target permanent' (not just one you control), it is a powerful tool for disrupting enemy strategies.

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