I like quite a bit more actually. I currently run:
The Infiltrator has good stats for its cost and evasion, and flash is a really nice ability when you're holding up a two mana counterspell.
Deepfathom Skulker buries your opponents in card advantage if you have monsters that can connect, and it can also make your guys unblockable to break board stalls.
Essence Depleter has decent stats, and the lifeleech adds up if you manage multiple colorless sources. Also good in board stalls.
The Shrieker is a tremendous attacker, often trading 2 for 1 if they have to block it because you can pump it. And if they can't block it it's rapidly turning a race in your favor.
Mindmelter breaks board stalls and has a relevant activated ability. It's been quietly good in the games I tried so far. Never spectacular, but much more solid than I had anticipated.
I'm suprised you didn't mention Reality Smasher. Not interested in a giant beatstick with some insurance in case your opponent has to kill it with a spell?
Endbringer untaps
every upkeep. Took me a while before I saw that. Giant beating if it lives!
Spatial Contortion is a solid removal spell that's useful for all the archetypes, and a good reward for accomodating colorless in your mana base.
And then I filled in some spots with customs to get every color up to two
cards. I didn't really like the red options, white only had one option, and
Worldbreaker wasn't really what I was looking for in green. These are quite simple designs, partly based of snow permanents from Coldsnap, that just fill in a few things I like to call "design holes"
Red was lacking artifact removal, some people felt
Flametongue Kavu was borderline too powerful (I cut it for that reason before actually, so I can't really disagree), and green lacked something to counteract flyers, maybe still does (this is just one card, after all).