Frilled Basilisk - It's fairly costed, though I'm not sure it needs to pump itself when it's blocked. 4 toughness is pretty resilient as it is, and the defending player will only ever send one creature to block it. Either way I see this card as an uncommon that would be a pretty good pull in limited.
Mirrorplasm GWUB
Creature - Ooze (M)
Hexproof
Each other permanent with a +1/+1 counter on it is a 0/0 Ooze creature with no abilities
Graft 4
0/0
Withered Lotus0
Artifact (R) T, Sacrifice Withered Lotus: Add CCC to your mana pool. You can't spend this mana to cast spells. "What are these dried flowers for?"
"Oh! To brew mana tea!"
Urza's Desert Lair
Land - Urza's Desert Lair [R]
When Urza's Desert Lair enters the battlefield, return a non-Lair land you control to its owner's hand. T: Add C. 6,T: Create a 2/2 colorless Sand Assembly-Worker creature token.
Archaic Blast deals 2 damage to any target.
Research 2R(While you're searching your library, you may reveal up to one card with research from your library and pay its research cost. If you do, put that card into your hand.)
Mossboulder Troll1GG
Creature - Troll (U) 1: Until your next turn, Mossboulder Troll becomes an artifact creature and gains defender and indestructible. He can turn into a stone at will. Changing back is the hard part. 3/4
I like the flavor of it a lot, although I don't think the defender does much of anything, since you can activate the ability while the creature is already attacking (right?). Because of that, I'd think it's a more of a rare than an uncommon.
Here's a crazy idea I just had:
Glimmering WeirdEE
Creature - Weird Elemental (R)
When Glimmering Weird enters the battlefield, you get EE
When Glimmering Weird leaves the battlefield, you lose EE
Legendary Creature - Spirit Knight (M)
Whenever you cast a spell, put a +1/+1 counter on Baron Sixtus VI.
At the beginning of your upkeep, draw a card if Baron Sixtus VI has two or more +1/+1 counters on it, then draw a card if Baron Sixtus VI has four or more +1/+1 counters on it, then draw a card if Baron Sixtus VI has six or more +1/+1 counters on it.
1/1
Next: A commander that either is a Wall or interacts with Walls in a flavorful way.
Creature - Human Knight (U)
Vigilance
Absorb X, where X is the number of Knight creatures you control. (If a source would deal damage to this creature, prevent X of that damage.)
2/2
Creature - Spirit Cleric (R)
When Spectral Inquisitor enters the battlefield, exile target nonland permanent until Spectral Inquisitor leaves the battlefield.
Unearth 2W(2W: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the end step or if it would leave the battlefield. Unearth only as a sorcery.)
2/3
Land (C)
Monument to Justice enters the battlefield tapped. T: Add 1 to your mana pool. T: Add 2 to your mana pool. Spend this mana only to cast your Commander from the command zone.
Sorcery (R)
Search your library for a creature card with no abilities and put it onto the battlefield. Shuffle your library afterward. "I need no rare or tamed beasts; only big ones." - Garruk Wildspeaker
Mirrorplasm GWUB
Creature - Ooze (M)
Hexproof
Each other permanent with a +1/+1 counter on it is a 0/0 Ooze creature with no abilities
Graft 4
0/0
River of Sorrows
Land (R)
T: Add C. If you played a land this turn, add U or B instead.
Artifact (R)
T, Sacrifice Withered Lotus: Add CCC to your mana pool. You can't spend this mana to cast spells.
"What are these dried flowers for?"
"Oh! To brew mana tea!"
Blank Lotus
Homunculotus
Lotus Wrap
Urza's Desert Lair
Land - Urza's Desert Lair [R]
When Urza's Desert Lair enters the battlefield, return a non-Lair land you control to its owner's hand.
T: Add C.
6,T: Create a 2/2 colorless Sand Assembly-Worker creature token.
Archaic Blast R
Instant - Arcane (C)
Archaic Blast deals 2 damage to any target.
Research 2R (While you're searching your library, you may reveal up to one card with research from your library and pay its research cost. If you do, put that card into your hand.)
With Fist of Suns out, Ramos' second ability allows you to cast any two spells you want.
I like the flavor of it a lot, although I don't think the defender does much of anything, since you can activate the ability while the creature is already attacking (right?). Because of that, I'd think it's a more of a rare than an uncommon.
Here's a crazy idea I just had:
Glimmering Weird EE
Creature - Weird Elemental (R)
When Glimmering Weird enters the battlefield, you get EE
When Glimmering Weird leaves the battlefield, you lose EE
2/2
EDIT: Halved everything to 2.
Dryad's Touch 1G
Enchantment - Aura (U)
Enchant creature
Enchanted creature is a Treefolk with base power and toughness 4/4 and loses all abilities.
Legendary Creature - Spirit Knight (M)
Whenever you cast a spell, put a +1/+1 counter on Baron Sixtus VI.
At the beginning of your upkeep, draw a card if Baron Sixtus VI has two or more +1/+1 counters on it, then draw a card if Baron Sixtus VI has four or more +1/+1 counters on it, then draw a card if Baron Sixtus VI has six or more +1/+1 counters on it.
1/1
Next: A commander that either is a Wall or interacts with Walls in a flavorful way.
Samite Cavalier WW
Creature - Human Knight (U)
Vigilance
Absorb X, where X is the number of Knight creatures you control. (If a source would deal damage to this creature, prevent X of that damage.)
2/2
Spectral Inquisitor 2W
Creature - Spirit Cleric (R)
When Spectral Inquisitor enters the battlefield, exile target nonland permanent until Spectral Inquisitor leaves the battlefield.
Unearth 2W (2W: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the end step or if it would leave the battlefield. Unearth only as a sorcery.)
2/3
Monument to Justice
Land (C)
Monument to Justice enters the battlefield tapped.
T: Add 1 to your mana pool.
T: Add 2 to your mana pool. Spend this mana only to cast your Commander from the command zone.
Primal Summoning 3G
Sorcery (R)
Search your library for a creature card with no abilities and put it onto the battlefield. Shuffle your library afterward.
"I need no rare or tamed beasts; only big ones." - Garruk Wildspeaker
Soil's Blessing XBG
Sorcery (R)
Discard your hand, then return up to X target cards from your graveyard to your hand.