Hi I'm Muirhead who previously wrote a Top8Patron guide.
Here is my take on the recently popular secret paladin, which I piloted to rank 4 NA legend:
I then proceeded to win five games in a row at rank 4 and then lose one all while staying at rank 4! I've never lost a game and maintained the same rank before.
I don't have anything as refined to say about this deck as I did for my patron list, because I only have 63 games recorded with this exact list! However, a few comments are in order.
Mulligans: Keep 1 and 2 mana minion drops and the mysterious challenger. Throw away all secrets, even if you have secret keeper. Keep divine favor only if you strongly suspect you are playing handlock or freeze mage. When playing against rogue, toss juggler in favor of a more sticky 2 drop. Depending on the MU and hand it is often good to keep muster as well.
This deck is very aggressive but has almost no reach, so it plays a lot like demonzoo. At some point you will have to try to rush face, usually after playing the 6 drop. Like demonzoo, when ahead on board it is important to play sticky minions against potential board clears.
The game plan is to flood the board in the early turns and get in some damage. If you draw shredder you can win just from this early aggression, but most of the time you will need to draw a divine favor or mysterious challenger by turn 6 or 7. Either of these cards will draw an immense amount of value, giving the reach you need to finish the game.
The challenger is both amazingly strong and it thins the bad draws from your deck. If possible, try to engineer maximum draw when you play the challenger: don't have a secret in play already that you can draw the second copy of from your deck.
The most unvaforable MU for the deck is face hunter with double explosive trap, which races you aggressively. Other unfavorable MUs include freeze mage and patron warrior. In my small sample size and testing I have a very good winrate vs all other decks.
Repentance is very key to play carefully in certain matchups. It is your #1 tool vs handlock and patron. On turns 5 and 6 patron might want to make a set of 4 patrons on an empty board to crush you, but he cannot play patron when repentance is up. Against handlock, if you set them below 10 HP when repentance is up they cannot play molten giant.
Edit: After a lot of playing and watching people play this deck I have some gameplay tips. I saw a lot of people losing against other paladins to consecration. Most of them were playing far too aggressively and not trading enough. Most paladins have no reach, so board control is much much more important than face damage in the matchup. My other tip is that a naked mysterious challenger is much weaker than a mysterious challenger supported by minions. If you have the choice between flooding the board effectively (i.e. using all your mana on sticky minions) and playing challenger it is sometimes correct to hold off on the challenger for one turn.
Possible tech choices: To improve the matchup against aggro and weaken it vs control, switch leper gnomes for squires. An early game leper gnome against a control deck often translates into about 4 more damage than an early game squire, and it's a much better topdeck late game vs control. However, in the mirror squires are better.
If you feel you are suffering for late game reach with this deck, consider switching one copy of competitive spirit for truesilver champion, a buff, or a big minion. The two weaker secrets in this style of deck are competitive spirit and redemption. If you do decide to run kings, squires become better.
My current version of the deck runs one less leper gnome, repentance, redemption, and competitive spirit. In their place I use coghammer, Loatheb, and 2x blessing of kings.
By request I've linked to some amazingly well-produced video guides to the deck. Not all of them showcase perfect play but they'll give good ideas of how the general gameplan works!