Zareth San, the Trickster — ruling 1

Before blockers are declared, attacking Rogues are neither blocked nor unblocked, so you can't pay the cost to activate Zareth San's second ability.

Zareth San, the Trickster — ruling 2

To activate Zareth San's second ability, you reveal it in your hand. It remains revealed until the ability has resolved.

Zareth San, the Trickster — ruling 3

If Zareth San leaves your hand before its second ability resolves, the ability does nothing as it resolves. Zareth San remains in its new zone and the Rogue you returned remains in its owner's hand.

Zareth San, the Trickster — ruling 4

You choose which player or planeswalker Zareth San is attacking. It doesn't have to be attacking the same player or planeswalker that the returned Rogue was attacking.

Zareth San, the Trickster — ruling 5

Although Zareth San is attacking, it was never declared as an attacking creature (for purposes of abilities that trigger whenever a creature attacks, for example).

Zareth San, the Trickster — ruling 6

Zareth San's second ability can be activated during the declare blockers step, combat damage step, or end of combat step. If you wait until after the declare blockers step, because all combat damage is dealt at once, Zareth San won't normally deal combat damage.

Zareth San, the Trickster — ruling 7

If a creature in combat has first strike or double strike, you can activate Zareth San's second ability during the first-strike combat damage step. Zareth San will deal combat damage during the regular combat damage step in this case, even if it somehow gains first strike.

Zareth San, the Trickster — ruling 8

In a multiplayer game, if a player leaves the game, all cards that player owns leave as well. If you leave the game, any permanents you control from Zareth San's last ability are exiled.

Zareth San, the Trickster : règles, fonctionnement et interactions (MTG)

Zareth San, the Trickster 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

Flash , Return an unblocked attacking Rogue you control to its owner's hand: Put this card from your hand onto the battlefield tapped and attacking. Whenever Zareth San deals combat damage to a player, you may put target permanent card from that player's graveyard onto the battlefield under your control.

How it works : Zareth San, the Trickster

Original English text — Wizards of the Coast / Scryfall

#1September 25, 2020· Wizards of the Coast
Before blockers are declared, attacking Rogues are neither blocked nor unblocked, so you can't pay the cost to activate Zareth San's second ability.
No other card is named in this ruling.
#2September 25, 2020· Wizards of the Coast
To activate Zareth San's second ability, you reveal it in your hand. It remains revealed until the ability has resolved.
No other card is named in this ruling.
#3September 25, 2020· Wizards of the Coast
If Zareth San leaves your hand before its second ability resolves, the ability does nothing as it resolves. Zareth San remains in its new zone and the Rogue you returned remains in its owner's hand.
No other card is named in this ruling.
#4September 25, 2020· Wizards of the Coast
You choose which player or planeswalker Zareth San is attacking. It doesn't have to be attacking the same player or planeswalker that the returned Rogue was attacking.
No other card is named in this ruling.
#5September 25, 2020· Wizards of the Coast
Although Zareth San is attacking, it was never declared as an attacking creature (for purposes of abilities that trigger whenever a creature attacks, for example).
No other card is named in this ruling.
#6September 25, 2020· Wizards of the Coast
Zareth San's second ability can be activated during the declare blockers step, combat damage step, or end of combat step. If you wait until after the declare blockers step, because all combat damage is dealt at once, Zareth San won't normally deal combat damage.
No other card is named in this ruling.
#7September 25, 2020· Wizards of the Coast
If a creature in combat has first strike or double strike, you can activate Zareth San's second ability during the first-strike combat damage step. Zareth San will deal combat damage during the regular combat damage step in this case, even if it somehow gains first strike.
No other card is named in this ruling.
#8September 25, 2020· Wizards of the Coast
In a multiplayer game, if a player leaves the game, all cards that player owns leave as well. If you leave the game, any permanents you control from Zareth San's last ability are exiled.
No other card is named in this ruling.