Two ways to go here: A weird pest tribal or a graveyard deck… or a combination of the two.
As has been documented pretty well, I like to play somewhat underpowered value decks full of cards you’d see in constructed midrange decks. For this specific purpose, the backside of the card is actually much stronger, but I’ll take the front side into account in this as well, because the lower casting cost might mean that you might want to play it at times. It can also function as a sort of weird and weak [card]Overrun[/card] if you have a lot of creatures on the battlefield and I’m going to try to go wide for specifically this purpose.
Let’s start with creatures and ways to make creatures:
Arasta of the Endless Web
Brood of Cockroaches
Mazirek, Kraul Death Priest
While I do regularly play some of these cards (I like cheap deathtouch creatures just because your opponents don’t want to trade their creatures for them), these are not the strongest cards out there, but for a deck with a lower powerlevel, this is a good start.
Next, some ways to abuse the cards that are going to be in our graveyard if we mostly want to use the backside:
[draft]Meren of Clan Nel Toth
The Gitrog Monster
Savra, Queen of the Golgari
How about some sacrificing?
[draft]Yawgmoth, Thran Physician
Sidisi, Undead Vizier
Tergrid, God of Fright
Rise of the Dread Marn
Liliana, Dreadhorde General[/draft]
I decided to go easy and not put in cards like [card]Dictate of Erebos[/card] to keep the deck casual.
We might need some lifegain as well, because the [card]Search for Blex[/card] can be expensive in the long term.
[draft]Gray Merchant of Asphodel
How about actually trying to kill our opponent at some point? Of course, this is purely optional.
[draft]Syr Konrad, the Grim
Vito, Thorn of the Dusk Rose
Thrown in 40 lands and were there. Again, not the strongest deck out there, but more for a casual table.