Innistrad: Midnight hunt

Adeline, Resplendent Cathar
Very neat because it plays well into the fact that cubelets are often played as a multiplayer format.

Brutal Cathar
Possibly an upgrade if you are playing Fiend Hunter. The opportunity for multiple flips is one to consider.

Fateful Absence
Very nice removal spell. Great option to consider.

Intrepid Adversary
Very strong late game to help push those last points of damage in.

Malevolent Hermit
There's a lot here that supports cubelets. So many options and implications, definitely a card to consider.

Spectral Adversary
A great way to keep your biggest threat around in response to a boardwipe. Even greater late game.

Suspicious Stowaway
Interesting replacement for Looter if you don't have one. The flip side is just a raw draw, which is always nice.

Champion of the Perished
If you are building a spooky cubelet or some other themed idea that involves zombies, this is probably a great include.

Jerren, Corrupted Bishop
Game play is interesting enough to consider.

The Meathook Massacre
A unique opportunity as a flexible board wipe that can get around pesky indestructible creatures.

Tainted Adversary
Like the other adversaries, this is a fun opportunity.

Bloodthirsty Adversary
Adversaries are good and should be fun to try.

Reckless Stormseeker
Great aggressive creature with a great ability on either side.

Primal Adversary
I can't stress this enough, this cycle is good for cubelet and you have lots of opportunity here to try out a few.

Arlinn, the Pack's Hope
Probably too good for cubelet. If you are willing to try it, go for it.

Crackling Counterpart
Funny card, funny way of snagging a creature with sweet abilities.

Florian, Voldaren Scion
The play clause on this means that you can play the card you exile as the land for turn if you didn't have the ability to play it for real.

Siphon Insight
A very interesting way to essentially draw a card because you aren't getting any other kind of advantage since you all share the same library.