Secret Paladin decks are still evolving and there are two types floating around: Aggro and Midrange. This version of the deck is more midrange, it includes powerful late game cards like Dr. Boom and Tirion Fordring, but still has aggressive early game cards like Argent Horserider. The deck also includes Blood Knight which is a solid card in the mirror match, and can just becomes a monster on the board if necessary. Mysterious Challenger is of course the catalyst of the whole deck, and this version of the deck runs one less Competitive Spirit than your typical aggro version.
Check out the more Aggressive Secret Paladin Deck.