Imagine the situation:
- I am at 2 life;
- I have five Forests untapped in the battlefield;
- I have 4 Giant Growth and 1 Become Immense in my hand;
- I have a Brainstorm in my graveyard;
- I have a 1/1 creature with no abilities
- My opponent has 19 life;
- My opponent has a 2/2 creature with no abilities.
I attack with my creature without casting any cards. My opponent doesn't block. Can I cast the 4 Giant Growths (+12/+12) using four of my five Forests and then cast the Become Immense (giving me a total of +18/+18) delving the four Giant Growth and the Brainstorm using the last Forest?