Hearthpwn

Something to replace Dr. Boom, Loatheb and Ragnaros the Firelord? Only these cards I don't have and I know they're good but I don't have dust for them :/

What shall i replace Rag and N'Zoth 

I can't replace Ragnaros the Firelord cuz this is unique creature with removal in the end of your each turn. This card can win ur game by lethal dmg in face or remove hard creature. It's very unique. e.g Baron Geddon is a very very bad replacement.
Same with N'Zoth, the Corruptor. 
N'Zoth it's your second plan to win. It's the same second plan to win, like Archmage Antonidas in tempo mage, that can be replaced only by Ragnaros btw, but u can't take Antonidas for Paladin right?
Guys, i can replace Dr. Boom or even Tirion Fordring but I just can't replace core creatures like Mysterious Challenger , Ragnaros the Firelord or N'Zoth cuz this is Secret N'Zoth Paladin and Ragnaros is your Joker. This deck is senseless w/o this creatures. 

Subbed Coghammer and Aldor for Truesilver and Uldaman.

Why did you use Truesilver Champion  instead Coghammer?

Truesilver Champion is not worst than Coghammer. 
1st of all Truesilver is better as removal
Coghammer is good against aggro, but even against Shaman, C'Thun Druid and btw the most of decks like Control/etc. Warriors and Priests i find Truesilver Champion much better.
I recommend use Coghammer insted of Truesilver, only against frequent match ups with Hunters and Zoolocks.

I really like your version of Secret Paladin. As long Belcher Shredders and Tirion are good in this deck anyway N'Zoth may do his job. Gr8 idea, i think i will test it.

Thanks

Can you replace Rag? 

Sorry but it's very unique creature

Would you tech an Eater of Secrets for mirror and freeze mage?

i switch with repentance

Eater of Secrets is very weak. It works well against Secret Paladin that can makes him 7/9 cuz eats 6 secrets in one turn. 
Mirror Entity is easy to counter by mindgame.
If you add Eater of Secrets to deck just to eat Ice Block it will be pretty useless.
1st reason - Secret Paladin is the deck that don't have enough card draw to find Eater of Secrets just in time ( you just have to be lucky that makes this deck unstable )
2st reason - In wild mode freeze mage is very rare
3rd reason - Freeze mage is always will be the hardest match up for Secret Paladin cuz of huge amount of removals and the reason that S. Paladin don't have heal spells
4th reason - Eater of Secrets is absolutely useless against most of decks that makes it a dead card in your deck/hand
I recommend Eater only if your match ups always against S. Paladins.
Click here and see that i did't have a problems against mages
P.S. Sry for my English

Secretadins and Hunters have freaking stolen the meta. So Eater is a beast yo.

Keeper of Uldaman is very unique card, i can't replace it, but if you need a useful creature for this deck for 4 mana, i offer you Spellbreaker 

I got legend with secret pala in december w/o Keeper of Uldaman, i used Aldor Peacekeeper instead, i hope this advice may help.

is enought with only 1 Mysterious Challenger?

If u lucky enough to always drop it on 6th turn.
I think u can try it, but better play with second Mysterious Challenger