Junk Golem 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

This creature enters with three +1/+1 counters on it. At the beginning of your upkeep, sacrifice this creature unless you remove a +1/+1 counter from it. , Discard a card: Put a +1/+1 counter on this creature.

Complete guide

Junk Golem is a versatile artifact creature that demands constant maintenance to stay on the battlefield. As a 0/0 base creature that enters with three +1/+1 counters, it serves as a flexible threat that you can fuel by discarding resources.

Maintenance and Upkeep

The core mechanic of Junk Golem is its upkeep trigger. At the start of your turn, you must choose between removing a +1/+1 counter from it or sacrificing the creature entirely. This means without intervention, the Golem will naturally last for three turns before it must be sacrificed or refueled.

Refueling the Golem

To keep the Junk Golem alive indefinitely or to grow it into a larger threat, you can use its activated ability. By paying one generic mana and discarding a card, you place a +1/+1 counter on it. This can be done at instant speed, allowing you to react to the upkeep trigger while it is still on the stack.

Resolving the Trigger

When your upkeep begins, the sacrifice trigger goes on the stack. You do not choose whether to remove a counter or sacrifice the creature until the ability actually resolves. If the Golem has no +1/+1 counters on it when the ability resolves, you must sacrifice it, as you cannot fulfill the requirement to remove a counter.

Strategic Timing

Since the activated ability doesn't require tapping, you can discard multiple cards in a single turn to make Junk Golem a massive attacker or blocker. It is often best to wait until the end of your opponent's turn or in response to the upkeep trigger to decide how many resources to commit.

Interaction examples

Doubling the Maintenance

Roaming Throne

If Roaming Throne enters and you choose 'Golem', Junk Golem's upkeep ability will trigger twice. This means you must remove two +1/+1 counters per turn (one for each trigger) or sacrifice it. While this drains counters faster, it also allows you to benefit more from other Golem-related triggers you might control.

Building a Large Attacker

If you have excess land cards in your hand, you can pay one mana and discard a land to put a +1/+1 counter on Junk Golem. You can repeat this process as many times as you have mana and cards, potentially turning a 3/3 into a 6/6 or larger in a single turn to overwhelm a blocker.

Golem Synergy

Solemn Simulacrum

In a deck featuring Solemn Simulacrum, you can use the extra land provided by the Simulacrum to afford the activation cost of Junk Golem. If Junk Golem is forced to sacrifice itself during upkeep because you have no counters left, it simply goes to the graveyard, but unlike Solemn Simulacrum, it does not provide a card draw benefit upon death.

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