If you control more than one Giant, Squash’s cost is reduced by only {3}.

Once you announce that you’re casting Squash, no player may take other actions until the spell’s been paid for. Notably, players can’t try to change the cost by removing your Giants.

Squash : règles, fonctionnement et interactions (MTG)

Squash 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

This spell costs less to cast if you control a Giant. Squash deals 6 damage to target creature or planeswalker.

How it works : Squash

Original English text — Wizards of the Coast / Scryfall

#1February 5, 2021· Wizards of the Coast
If you control more than one Giant, Squash’s cost is reduced by only .
No other card is named in this ruling.
#2February 5, 2021· Wizards of the Coast
Once you announce that you’re casting Squash, no player may take other actions until the spell’s been paid for. Notably, players can’t try to change the cost by removing your Giants.
No other card is named in this ruling.