Inspired Idea

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.

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

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.

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.

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.

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.