Inspired Idea — ruling 1

If a player has more cards in their hand than their maximum hand size during the cleanup step of that player's turn, that player discards until they have that many cards. A player's maximum hand size isn't checked at any time other than their own cleanup step.

Inspired Idea — ruling 2

If multiple effects modify your hand size, apply them in timestamp order. For example, if you are affected by Null Profusion (an enchantment that sets a player's maximum hand size to two) and then resolve Inspired Idea without paying its cleave cost, your maximum hand size would be zero. However, if Null Profusion entered the battlefield after Inspired Idea resolved, your maximum hand size would be two.

Inspired Idea — ruling 3

If you currently have no maximum hand size, then reducing your maximum hand size by three will have no effect. If the effect causing you to have no maximum hand size ends, Inspired Idea's effect will apply at that time.

Inspired Idea — ruling 4

If you cast a spell for its cleave cost, that spell doesn't have any of the text in square brackets while it's on the stack.

Inspired Idea — ruling 5

A cleave cost is an alternative cost that's paid instead of the spell's mana cost. Casting a spell for its cleave cost doesn't change the spell's mana value.

Inspired Idea — ruling 6

You can't cast a spell for both its cleave cost and another alternative cost. For example, if an effect gives an Alchemist's Retrieval in your graveyard a flashback cost of {U}, you can't cast it from your graveyard for its cleave cost.

Inspired Idea — ruling 7

If an effect allows you to “cast a spell without paying its mana cost,” you can't cast that spell for its cleave cost.

Inspired Idea : règles, fonctionnement et interactions (MTG)

Inspired Idea 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

Cleave (You may cast this spell for its cleave cost. If you do, remove the words in square brackets.) Draw three cards. [Your maximum hand size is reduced by three for the rest of the game.]

How it works : Inspired Idea

Original English text — Wizards of the Coast / Scryfall

#1November 19, 2021· Wizards of the Coast
If a player has more cards in their hand than their maximum hand size during the cleanup step of that player's turn, that player discards until they have that many cards. A player's maximum hand size isn't checked at any time other than their own cleanup step.
No other card is named in this ruling.
#2November 19, 2021· Wizards of the Coast
If multiple effects modify your hand size, apply them in timestamp order. For example, if you are affected by Null Profusion (an enchantment that sets a player's maximum hand size to two) and then resolve Inspired Idea without paying its cleave cost, your maximum hand size would be zero. However, if Null Profusion entered the battlefield after Inspired Idea resolved, your maximum hand size would be two.
No other card is named in this ruling.
#3November 19, 2021· Wizards of the Coast
If you currently have no maximum hand size, then reducing your maximum hand size by three will have no effect. If the effect causing you to have no maximum hand size ends, Inspired Idea's effect will apply at that time.
No other card is named in this ruling.
#4November 19, 2021· Wizards of the Coast
If you cast a spell for its cleave cost, that spell doesn't have any of the text in square brackets while it's on the stack.
No other card is named in this ruling.
#5November 19, 2021· Wizards of the Coast
A cleave cost is an alternative cost that's paid instead of the spell's mana cost. Casting a spell for its cleave cost doesn't change the spell's mana value.
No other card is named in this ruling.
#6November 19, 2021· Wizards of the Coast
You can't cast a spell for both its cleave cost and another alternative cost. For example, if an effect gives an Alchemist's Retrieval in your graveyard a flashback cost of , you can't cast it from your graveyard for its cleave cost.
No other card is named in this ruling.
#7November 19, 2021· Wizards of the Coast
If an effect allows you to “cast a spell without paying its mana cost,” you can't cast that spell for its cleave cost.
No other card is named in this ruling.