Midnight Clock — ruling 1

If Midnight Clock leaves the battlefield while its last ability is on the stack, it won't be exiled.

Midnight Clock — ruling 2

You can activate Midnight Clock's mana ability to pay the cost of its second ability.

Midnight Clock — ruling 3

Midnight Clock's last ability triggers after one or more counters are put onto it if it had fewer than twelve counters on it before those counters were put on it and it has twelve or more counters on it after.

Midnight Clock — ruling 4

Midnight Clock's first triggered ability triggers at the beginning of each upkeep, not just your upkeep. In a Two-Headed Giant game, an ability that triggers at the beginning of each upkeep rather than each player's upkeep triggers only once during each team's upkeep.

Midnight Clock : règles, fonctionnement et interactions (MTG)

Midnight Clock 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

: Add . : Put an hour counter on this artifact. At the beginning of each upkeep, put an hour counter on this artifact. When the twelfth hour counter is put on this artifact, shuffle your hand and graveyard into your library, then draw seven cards. Exile this artifact.

How it works : Midnight Clock

Original English text — Wizards of the Coast / Scryfall

#1October 4, 2019· Wizards of the Coast
If Midnight Clock leaves the battlefield while its last ability is on the stack, it won't be exiled.
No other card is named in this ruling.
#2October 4, 2019· Wizards of the Coast
You can activate Midnight Clock's mana ability to pay the cost of its second ability.
No other card is named in this ruling.
#3October 4, 2019· Wizards of the Coast
Midnight Clock's last ability triggers after one or more counters are put onto it if it had fewer than twelve counters on it before those counters were put on it and it has twelve or more counters on it after.
No other card is named in this ruling.
#4October 4, 2019· Wizards of the Coast
Midnight Clock's first triggered ability triggers at the beginning of each upkeep, not just your upkeep. In a Two-Headed Giant game, an ability that triggers at the beginning of each upkeep rather than each player's upkeep triggers only once during each team's upkeep.
No other card is named in this ruling.

Interactions with other cards

These cards' text mentions Midnight Clock.

Rusko, Clockmaker

When Rusko, Clockmaker enters the battlefield, conjure a card named Midnight Clock onto the battlefield. Whenever you cast a noncreature spell, put an hour counter on each permanent you control named Midnight Clock. Each opponent loses 1 life and you gain 1 life.