Primalcrux — ruling 1

This will count the number of symbols in its mana cost while it's on the battlefield. The ability functions while it's in other zones, but since it isn't a permanent while in those zones it won't count itself.

Primalcrux — ruling 2

Chroma abilities check only mana costs, which are found in a card's upper right corner. They don't count mana symbols that appear in a card's text box.

Primalcrux — ruling 3

Chroma abilities count hybrid mana symbols of the appropriate color. For example, a card with mana cost {3}{U/R}{U/R} has two red mana symbols in its mana cost.

Primalcrux : règles, fonctionnement et interactions (MTG)

Primalcrux 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

Trample Chroma — This creature's power and toughness are each equal to the number of green mana symbols in the mana costs of permanents you control.

How it works : Primalcrux

Original English text — Wizards of the Coast / Scryfall

#1August 1, 2008· Wizards of the Coast
This will count the number of symbols in its mana cost while it's on the battlefield. The ability functions while it's in other zones, but since it isn't a permanent while in those zones it won't count itself.
No other card is named in this ruling.
#2August 1, 2008· Wizards of the Coast
Chroma abilities check only mana costs, which are found in a card's upper right corner. They don't count mana symbols that appear in a card's text box.
No other card is named in this ruling.
#3August 1, 2008· Wizards of the Coast
Chroma abilities count hybrid mana symbols of the appropriate color. For example, a card with mana cost has two red mana symbols in its mana cost.
No other card is named in this ruling.