Chittering Host — ruling 1

The set of creatures affected by Chittering Host's triggered ability is determined as the ability resolves. Creatures you begin to control later in the turn won't get +1/+0 or gain menace.

Chittering Host — ruling 2

For more information on meld cards, see the Eldritch Moon mechanics article (https://magic.wizards.com/en/articles/archive/feature/eldritch-moon-mechanics-2016-06-27).

Chittering Host : règles, fonctionnement et interactions (MTG)

Chittering Host 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

Haste Menace (This creature can't be blocked except by two or more creatures.) When this creature enters, other creatures you control get +1/+0 and gain menace until end of turn.

How it works : Chittering Host

Original English text — Wizards of the Coast / Scryfall

#1July 13, 2016· Wizards of the Coast
The set of creatures affected by Chittering Host's triggered ability is determined as the ability resolves. Creatures you begin to control later in the turn won't get +1/+0 or gain menace.
No other card is named in this ruling.
#2July 13, 2016· Wizards of the Coast
For more information on meld cards, see the Eldritch Moon mechanics article (https://magic.wizards.com/en/articles/archive/feature/eldritch-moon-mechanics-2016-06-27).
No other card is named in this ruling.

Interactions with other cards

These cards' text mentions Chittering Host.

Graf Rats

At the beginning of combat on your turn, if you both own and control this creature and a creature named Midnight Scavengers, exile them, then meld them into Chittering Host.