Caller of the Unknown —
Creature — Human Shaman (R)
Whenever Caller of the Unknown attacks, add to your mana pool. Then, you may cast a creature card from your hand as though it had flash. If you do, that creature enters the battlefield tapped and attacking.
1/1

My quest to create a printable card that allows me to swing for 8 on Turn 2 with my favorite card, Phyrexian Soulgorger, continues. This one swings for 9, AND leaves the creature around for you to sacrifice next turn!

Why not just "Then, you may cast a creature card [from your hand]. If you do, it enters the battlefield tapped and attacking."?
Is it necessary for the design that it can't be used to play creatures without generic or colorless mana cost?

I feel like Caller is overpowered... they did move mana elves from 1 mana to 2 mana, after all, and Caller is basically a mana elf. Somewhat more conditional, but with upside. Although, I could see it working if you instead sacrificed it to add the mana to your mana pool... or even if you just returned it to your hand as a sort of reverse ninjitsu.

Hunter's Flare —
Instant (U)
Add to your mana pool. If that mana is spent on a creature spell, it gains haste.
Draw a card.
Garruk had to admit, the torches Chandra had turned him on to were really quite useful.

Simic Mimic —
Creature — Shapeshifter Ooze
Simic Mimic enters the battlefield with a +1/+1 counter on it.
You may have Simic Mimic enter the battlefield as a copy of any creature on the battlefield.
Momir Vig was always eager to improve on others' work.
0/0

Garden Terror —
Creature — Plant Zombie (U)
Sacrifice Garden Terror: Return target land card from your graveyard to the battlefield.
"Rise, my beautiful children! Bring death to all those who would challenge your vigorous life, and leave their corpses strewn in the valley of your spores."
—Hell-Cath, the Gravetender
2/2

Big fan of your Hell-Cath inspired design!

I thought it was hots inspired.

It's both.

Dirge of the Damned —
Sorcery (R)
Dirge of the Damned deals 4 damage to each creature.
Return target creature from a graveyard to the battlefield under your control.
Madness
"Round and round the fires swarmed,
Hotter than the hell flames,
But what was worse was what dispersed
From ashes when the dead came."

Song of the Sea —
Instant (U)
Counter target spell.
Draw a card, then discard a card.
"There was a time
When salty brine
Did flow the other way.
In seven years
Thalassa's tears
Will rise up from the clay."
—Merfolk prophecy

This won't let you bring back a creature you just killed

Sunken Sorcerer —
Creature — Naga Shaman
Deathtouch
: Add to your mana pool. Activate this ability only if there is a creature card in your graveyard.
: Add to your mana pool. Activate this ability only if there is a land card in your graveyard.
: Add to your mana pool. Activate this ability only if there is an instant or sorcery card in your graveyard.
1/2

Hordecaller —
Creature — Goblin Berserker
As long as Hordecaller is attacking, you may cast creatures from your hand as though they had flash. If you do, they enter the battlefield tapped and attacking.
2/1

Wow, this is f...ing nuts.

Elite Vanguard plus Fervor plus "creatures that entered the battlefield this turn can't be blocked" and all of that for 1 hybrid (!) mana.

love it. but probably or even . With uselesscommon here.

how about if it were a 3/2 for ?

Hexed Bolt —
Instant
As long as your life total is exactly 13, Hexed Bolt costs less to cast.
Hexed Bolt deals 4 damage to target creature or player.

More like a 2/2 for

Does it really prevent the creatures from being blocked, though? The haste is definitely intentional, but you can block stuff created by Militia's Pride and Yore-Tiller Nephilim, can't you? Why not this?

Word it as "When ~ attacks, you may cast any number of creatures from your hands. If you cast any creatures this way, they enter the battlefield tapped and attacking."

That way you avoid the mess of putting things tapped and attacking during the blocker step or anything.