The Flux There are quite a few four-mana red cards that exist in similar space to The Flux, slowly generating card advantage over time with impulsive card draw, as they call it
Elsewhere in the world of gaming, check out the indy100 reviews of Avowed and Tomb Raider IV-VI Remastered
For decks with three or more colors, where you might only be able to afford a small number of MDFCs since you'll need most of your lands to either be basics (for ramping / tutoring purposes) or tap for multiple colors of mana, the best MDFCs are Bala Ged Recovery (seriously, if you have green mana in your deck, play this card), Valakut Awakening, Hagra Mauling, and Ondu Inversion, along with the mythic cycle, which is almost always good if you can afford another land that only taps for a single color of mana
Auctions are best saved for scarce or hot cards, where competing bidders push the final price past what a fixed listing would get
Or if you don't have it out but have a large army, you can turn a random 1/1 into a serious threat