As you achieve minor weekly quests, such as inflicting X amount of damage or casting X number of spells of a certain color, you earn in-game gold that can be spent on slowly acquiring more booster packs, which you can open to earn a handful of randomly-generated cards
Honorable Mention - Shock Lands The return of shock lands is big for mana aggression, as each card allows you to place a dual color land untapped at the cost of two life points , or it can enter tapped with no charge
Once you have Adaptive Training Post out with at least two counters on it you can go ahead and cast a spell to put that third counter on the Post
Similarly, the modality of Boros Charm means that, though dealing 8 doesnt help us clear that first gate, the indestructible board or ability to give Lightning Double Strike make it a highly useful card
The only problem is that its almost impossible to find, with decks selling out instantly and releases being plagued with other problems