During their turn, they can burn them (use them and return them to their reserve) to activate cards, or flare them (flip them to their dark side) to exceed their burn limit, at the cost of leaving them unusable until they are refreshed (usually by discarding cards)
However, you won't be able to use fake Magic cards or proxies in competitive events, unless the event says otherwise for price-heavy formats like Vintage, where it's usually allowed to use some proxies to avoid damaging the original cards, as long as you own them
If you've already got the card, then you can still enjoy some vault progress
All three modes were really strong, as the +2/+2 mode made it really difficult for your opponent to block, the -1/-1 mode effectively shut down Creatures with two or less toughness, and the life gain could help you stabilize against aggressive decks
A clever opponent might try and bait out your removal with a threatening flier to make a more significant play later on
You never ever play Anticipate if you could play Impulse instead