Withering Wall —
Creature — Plant Wall (C)
When Withering Wall dies, create an 0/2 green Plant Wall creature token with "When this creature dies, create an 0/1 green Plant Wall creature token."
"I could have sworn we cut it down yesterday! I'm always getting tripped up on that thing…"
—Hans, to Saffi
0/3

Brain Spank
Sorcery
Target opponent discards a card and loses 2 life.

Pick Brains
Sorcery
Draw two cards unless target opponent discards two cards.
"I know how to pick a winner... but you'll have to do."

Counteract
Instant (C)
Counter target permanent spell (Artifacts, creatures, enchantments and planeswalkers are permanents)

Crumbling Bones
Enchantment - Aura
Enchant creature
Enchanted creature gets -3/-3.

both the mechanics and the flavor text really, but I could be missing something

Mix Up

Instant
Target player shuffles their library.
Draw a card.

Large Goomba Zone
Sorcery
Choose one -
- Create two 1/1 brown Fungus creature tokens.
- Put a +1/+1 counter on each creature you control.
In reality, Goombas make poor soldiers - they are entirely unarmed.

Not sure how my brain came up with the name but it might have been because I thought of it when I got up for a wee at like 3:30am

Akki Pyromancer -
Creature - Goblin Wizard
Flash
When ~ enters the battlefield, it deals 4 damage to any target.
1/1


Mono red has only 7 flash creatures. I originally wanted to make "red's strong 2 drop" as a Volcanic Hammer stapled to a 1/1, but that was just a stronger version of Sparkmage Apprentice. I added flash since burn is better at instant speed, then made it cost 4 so it's harder to abuse with Restoration Angel etc.

Lack of Competition -
Enchantment
As long as you control two or fewer creatures, creatures you control get +3/+3.

Unminding
Sorcery (U)
Target player discards three cards.

Facts: Divination is nice, Concentrate is very good but not quite OP, Mind Rot is pretty bad, Fugue is unplayable. Based on those facts, it's weird that this card wasn't printed yet.

Ice Guard
Creature - Elemental (C/U)
2/5

Could also see this in White, or maybe even Black.

Knight of the Cudgel
Creature - Human Knight
"I hit, and I take hits. Anything else is just window dressing."
3/3

I suspect this isn't something they'd do since they probably consider 3/3s the domain of green

Ancestral Lotus -
Artifact
When ~ enters the battlefield, draw three cards.
Sacrifice ~: Add three mana of any one color.

Thorn and Spine
Instant
Put two +1/+1 counters on target creature.

Inertia Bolt
Instant (C)
Inertia Bolt deals 2 damage to target creature or 4 damage if that creature is tapped.

Mass Reclaim -
Sorcery
Put any number of target cards from your graveyard on top of your library in a random order.

Double Bob -
Sorcery
Reveal the top two cards of your library and put them into your hand. You lose life equal to their total converted mana cost.
Bite off more than you can chew.

Slaughter Time

Sorcery
Target creature gains haste and double strike until end of turn.

Autonomy -
Enchantment
Each Vehicle you control is a creature in addition to its other types.

how about narrow but efficiently costed cards, with inefficient cycling costs? E.g. if Break Asunder cost and was instant but had cycling

Salvage Rights
Sorcery
Return target artifact or creature card from your graveyard to your hand.
"Corpses? We drag 'em up fairly often. Rarely worth much, though - any fool can make 'em."
- Docherty, Coal Pit Lake trawler

Ancient Tales
Sorcery
Return target creature or enchantment card from your graveyard to your hand.
The best storytellers guide you to a place outside of time: where what you're hearing has happened, is happening, and could still happen again.