Primal Surge exiles cards from your library and puts permanents among them onto the battlefield until you choose to stop or reveal a nonpermanent. Decks built with Primal Surge as their only instant or sorcery can therefore place nearly the entire library onto the battlefield.
Haste enablers such as Concordant Crossroads can let the resulting army attack immediately, while Laboratory Maniac-style effects provide another way to exploit suddenly having essentially no library left.
