Cascade Seer — ruling 1

If there are no creatures in your party as Cascade Seer's ability resolves, you don't scry at all. Abilities that trigger whenever you scry don't trigger.

Cascade Seer — ruling 2

To determine “the number of creatures in your party,” check whether you control a Cleric, whether you control a Rogue, whether you control a Warrior, and whether you control a Wizard. The number is the total number of those checks to which you answered yes. Each creature you control can be counted for only one of those checks.

Cascade Seer — ruling 3

If a creature has more than one party creature type, and there are multiple ways to count that creature that could result in a different number of creatures in your party, the highest such number is used. For example, if you control a Cleric and a Cleric Wizard, the number of creatures in your party is two. You can't choose to have it be just one by counting the Cleric Wizard first as a Cleric.

Cascade Seer — ruling 4

An ability referring to the number of creatures in your party gets a number from zero to four. Such abilities never ask which creatures are in your party, and you never have to designate specific creatures as being in your party. You can't choose to exclude creatures from this count to lower the number.

Cascade Seer — ruling 5

If an ability of a creature counts the number of creatures in your party, that number is counted as the ability resolves. If that creature is still on the battlefield when the ability resolves, it'll be counted if appropriate.

Cascade Seer : règles, fonctionnement et interactions (MTG)

Cascade Seer 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

When this creature enters, scry X, where X is the number of creatures in your party. (Your party consists of up to one each of Cleric, Rogue, Warrior, and Wizard.)

How it works : Cascade Seer

Original English text — Wizards of the Coast / Scryfall

#1September 25, 2020· Wizards of the Coast
If there are no creatures in your party as Cascade Seer's ability resolves, you don't scry at all. Abilities that trigger whenever you scry don't trigger.
No other card is named in this ruling.
#2September 25, 2020· Wizards of the Coast
To determine “the number of creatures in your party,” check whether you control a Cleric, whether you control a Rogue, whether you control a Warrior, and whether you control a Wizard. The number is the total number of those checks to which you answered yes. Each creature you control can be counted for only one of those checks.
No other card is named in this ruling.
#3September 25, 2020· Wizards of the Coast
If a creature has more than one party creature type, and there are multiple ways to count that creature that could result in a different number of creatures in your party, the highest such number is used. For example, if you control a Cleric and a Cleric Wizard, the number of creatures in your party is two. You can't choose to have it be just one by counting the Cleric Wizard first as a Cleric.
No other card is named in this ruling.
#4September 25, 2020· Wizards of the Coast
An ability referring to the number of creatures in your party gets a number from zero to four. Such abilities never ask which creatures are in your party, and you never have to designate specific creatures as being in your party. You can't choose to exclude creatures from this count to lower the number.
No other card is named in this ruling.
#5September 25, 2020· Wizards of the Coast
If an ability of a creature counts the number of creatures in your party, that number is counted as the ability resolves. If that creature is still on the battlefield when the ability resolves, it'll be counted if appropriate.
No other card is named in this ruling.