Almost all of them hover around the $1-2 range, which isnt particularly exciting for a Secret Lair card
Regarding Marang River Regent, there is a ton of value on one card
15 Darien, King Of Kjeldor Darien, King of Kjeldor is an extremely interesting commander due to the fact that he contorts one of the primary goals of your strategy
Having a burn spell you can often only cast post-combat is very awkward
When our Praetors enter the battlefield, we'll get Elesh Norn, Mother of Machines, which will double trigger Sheoldred to make our opponent sacrifice two creatures or planeswalkers, and also Vorinclex to tutor four Forests from our deck
And yet, Ive never been able to find a place for it in Commander, at least not as the main win condition