Magus of the Will doesn't change when you can play the cards in your graveyard. For example, if you have a creature card without flash in your graveyard, you can cast it only during your main phase while the stack is empty.

You pay the costs for a card in your graveyard if you cast it. You may pay alternative costs such as overload rather than the card's mana cost.

You may play a land card from your graveyard only if you have an available land play.

Cards that would be put into your graveyard are exiled even if you didn't play them this turn, such as a nontoken creature that would die.

Tokens are put into your graveyard as normal (and cease to exist soon after). Abilities that trigger when a creature dies can trigger on token creatures being put into your graveyard but won't trigger on nontoken creatures being exiled instead of being put into your graveyard.

If another effect tries to change where a spell is put as it resolves, such as that of a rebound or buyback ability, you may choose whether to exile the card to Magus of the Will's effect or to apply the other effect.