It is the third and final set of the Mirrodin block
Ardyn, the Usurper If youre building a demon typal deck, Ardyn, the Usurper might be your best pick for a commander
There's nothing wrong with playing staples and aiming for a higher power level, but there's also nothing wrong with getting cute with your synergy and having what might be a lower powered deck
Falkenrath Gorger gives any vampire card the madness text, while Conspiracy Theorist, Containment Construct and Oskar, Rubbish Reclaimer work for any card (though Theorist and Construct do not let you break timing rules the way true madness does)
For example, if you choose the second mode of Eldrazi Confluence more than once, you choose the relative order to exile and return the target nonland permanents