Nyx Weaver 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

Reach At the beginning of your upkeep, mill two cards. (Put the top two cards of your library into your graveyard.) , Exile this creature: Return target card from your graveyard to your hand.

Complete guide

Nyx Weaver is a versatile enchantment creature that fuels your graveyard strategies while acting as a defensive wall. This Spider not only fills your graveyard every turn but also offers a one-time escape hatch to retrieve any resource you might have lost.

A Consistent Engine

Nyx Weaver possesses two primary functions. First, its triggered ability occurs at the start of your upkeep, requiring you to mill two cards. Second, it has an activated ability that allows you to exile Nyx Weaver from your graveyard or the battlefield to return any card from your graveyard to your hand. Note that since it has Reach, it can also block creatures with flying, making it a solid defensive piece.

The Step-by-Step Resolution

During your upkeep, the mill ability goes on the stack automatically; you must put the top two cards of your library into your graveyard. The activated ability can be used at any time you have priority. When you pay the mana and exile Nyx Weaver, you choose a target card in your graveyard. As the ability resolves, that card moves to your hand. If the target becomes illegal before resolution, the ability fails and the card stays in the graveyard.

Strategic Timing

Because the sacrifice/exile ability is an activated ability, you can use it in response to an opponent's spell. However, once you exile Nyx Weaver to pay the cost, it is no longer on the battlefield to block. It is often best to wait until your opponent's end step or in response to removal to get the most value out of the recursion effect.

Avoiding Common Pitfalls

Remember that the mill ability is not optional; you must mill two cards every upkeep as long as Nyx Weaver is on the battlefield. Additionally, exiling Nyx Weaver is part of the cost of the recursion ability. If your opponent tries to remove it in response to you activating the ability, they are too late, as the creature is already exiled as a cost before they get priority.

Interaction examples

Recovering Lost Value

Solemn Simulacrum

If your Solemn Simulacrum was destroyed earlier in the game, you can activate Nyx Weaver by paying one black, one green, and one generic mana. By exiling Nyx Weaver, you can return Solemn Simulacrum to your hand, allowing you to cast it again for more land ramp and card draw.

Graveyard Synergy

Sakura-Tribe Elder

During your upkeep, Nyx Weaver mills a Sakura-Tribe Elder into your graveyard. Later, if you need a specific land that is still in your deck, you can exile Nyx Weaver to return the Sakura-Tribe Elder to your hand. You can then cast the Elder and sacrifice it to search for that land, turning your graveyard into an extended resource pool.

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