Do you need to cast a spell to take a card from the support pool? I'm assuming yes because certain spell have this as an option. You can't take cards from the support pool unless you cast a spell?
Every effect making you pay element cards allows you paying with cards in support:
- Buying upgraded element cards
- Discarding (healing) curses
- Buying new spells
- Activating spells
- Defeating curses
I feel there are more cases but my brain is fried right now. Also remember that cards taken from another players support goes to that players discard pile, not your own.