Cephalid Sage — ruling 1

You draw three cards and discard two cards all while Cephalid Sage’s ability is resolving. Nothing can happen between the two, and no player may choose to take actions.

Cephalid Sage — ruling 2

If you don’t have enough cards in your graveyard at the moment Cephalid Sage enters the battlefield, its threshold ability won’t trigger. If the number of cards in your graveyard changes and Cephalid Sage loses the ability once it has triggered, the ability will still resolve.

Cephalid Sage : règles, fonctionnement et interactions (MTG)

Cephalid Sage 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

Threshold — As long as there are seven or more cards in your graveyard, this creature has "When this creature enters, draw three cards, then discard two cards."

How it works : Cephalid Sage

Original English text — Wizards of the Coast / Scryfall

#1June 8, 2016· Wizards of the Coast
You draw three cards and discard two cards all while Cephalid Sage’s ability is resolving. Nothing can happen between the two, and no player may choose to take actions.
No other card is named in this ruling.
#2June 8, 2016· Wizards of the Coast
If you don’t have enough cards in your graveyard at the moment Cephalid Sage enters the battlefield, its threshold ability won’t trigger. If the number of cards in your graveyard changes and Cephalid Sage loses the ability once it has triggered, the ability will still resolve.
No other card is named in this ruling.