Myr PrototypeHow it works & interactions with other cards

Scaling Power and Costs

Myr Prototype has a triggered ability that occurs at the beginning of your upkeep, adding a +1/+1 counter to itself. While this makes it larger, it also increases the tax required for it to participate in combat. To declare it as an attacker or blocker, you must pay {1} for every +1/+1 counter currently on it. If you cannot or choose not to pay this total cost, the creature simply cannot be declared as an attacker or blocker for that phase.

Resolution Step-by-Step

First, the upkeep trigger is put on the stack; when it resolves, the counter is placed. Later, during the declare attackers or declare blockers step, you determine the total tax based on the counters present. This payment is a cost to declare the action, not an activated ability, so it does not use the stack and cannot be responded to once you begin declaring attackers or blockers.

Common Pitfalls

A frequent mistake is forgetting that the tax applies to both attacking and blocking. If you spend all your mana during your main phase to cast other spells, your Myr Prototype will be unable to block during your opponent's next turn if it has any counters. Additionally, if the counters are removed (via other card effects), the tax decreases immediately, as the check only happens at the moment you declare it as a combatant.

When to Play It

Myr Prototype is best suited for decks that can generate excess mana or those that benefit from high-powered artifact creatures. It serves as a growing wall that can eventually become a game-ending threat, provided you have the mana to unlock its potential during the combat phase.

Interaction examples

Accelerated Growth

Roaming Throne

If Roaming Throne enters the battlefield naming 'Myr', it will cause Myr Prototype's upkeep ability to trigger twice. This means you will put two +1/+1 counters on it each turn. While this doubles its growth speed, it also doubles the mana tax you must pay to attack or block each round.

Managing Resources

Solemn Simulacrum

Since Myr Prototype becomes more expensive to use as the game progresses, cards like Solemn Simulacrum are vital. The extra basic land provided by the Simulacrum helps ensure you have the necessary mana to pay the Prototype's attacking tax while still being able to cast other spells during your turn.