Graverobber Spider — ruling 1

The number of creature cards in your graveyard is counted only as the ability resolves. Once the ability resolves, the bonus won't change, even if the number of creature cards in your graveyard changes later in the turn.

Graverobber Spider : règles, fonctionnement et interactions (MTG)

Graverobber Spider 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 : This creature gets +X/+X until end of turn, where X is the number of creature cards in your graveyard. Activate only once each turn.

How it works : Graverobber Spider

Original English text — Wizards of the Coast / Scryfall

#1February 1, 2014· Wizards of the Coast
The number of creature cards in your graveyard is counted only as the ability resolves. Once the ability resolves, the bonus won't change, even if the number of creature cards in your graveyard changes later in the turn.
No other card is named in this ruling.