Paying the Right Price -
Instant
Kicker
Destroy target creature. If ~ kicker's cost was paid, exile that creature instead. Otherwise, that creature's controller creates two 1/1 white green citizen creature tokens.
It is always good insurance to pay extra for the extra lives that needs silencing.

Pay the Piper
Enchantment - Aura (U)
Enchant player
Enchanted player has "Whenever a creature enters the battlefield under your control, you may pay any amount of mana. You lose X life, where X is that creature's mana value minus the amount of mana you paid."

Revel Piper
Creature — Satyr Bard
, Put a stun counter on a land you control without a stun counter: Add or .
"Xenagos's reign was brief, but what a reign."
1/1

Put That in Your Pipe and Smoke It
Sorcery
Sacrifice an artifact. Then, if you control an artifact, add .

Sovereign of Smokeless Flame
Creature — Efreet Noble
If an instant or sorcery spell you control would deal damage to an opponent or a permanent an opponent controls, instead create that many tapped Treasure tokens.
At the beginning of your end step, sacrifice all untapped Treasures you control.
"I will bend to no god."
3/3

Flaming Bear
Creature - Elemental Bear
Ward - Pay X life, where X is this creature's power.
: ~ gets +1/+0 until end of turn. If this was the second time this ability was activated this turn, ~ gets first strike until end of turn. If it was the third time, ~ gets trample until end of turn.
"As the one responsible for incurring its wrath, only you can appease the forest's fire," - Smo'Ke, Forest Hermit.
[2/2]

Bear Witness
Creature - Bear Clue
, Sacrifice Bear Witness: Draw a card.
2/2

Witness Atrocities
Enchantment - Aura
Enchant creature
Enchanted creature has "Whenever another creature you control dies, you lose 2 life".
What is worse - to perish with the rest, or be the only one left standing?

Kill the Beast!
Instant (u)
Destroy target tapped creature with power 4 or greater.
"It's a beast, he's got fangs razor sharp ones.
Massive paws, killer claws for the feed.
Hear him roar, see him foam,
But we're not coming home,
'Till he's dead, good and dead..."

Killer App

Enchantment - Aura
Enchant Artifact
Enchanted artifact has "Whenever a creature deals combat damage to you, that creature's controller gains control of this permanent"
Everybody wants it.

Apply for Virtue
Instant
~ costs less to cast if you control a background.
~ deals 3 damage to any target and you gain 3 life. If you control a legendary creature that you own, that creature gets protection from noncreature spells until the beginning of your next turn.
"While I find the motivations of my ... 'allies' ... to be questionable, I will not judge them too harshly as long as they help me serve Tempus faithfully.

Uncommon Virtue
Instant
Reveal your hand and exile all cards with madness from it and from your graveyard. You draw X cards and gain X life, where X is the number of cards exiled from your hand this way plus one.
Madness
"Many fall in the face of chaos, but not this one. Not today." — The Ancestor

Commoners' Revolt —
Sorcery (R)
Commoners' Revolt deals damage equal to the number of creature tokens you control to each nontoken creature.

Revolting Ghoul
Creature — Zombie
Creatures with -1/-1 counters you control have menace.
4/2

Ghoul Lash
Artifact - Equipment Food
Equipped creature has first strike.
Whenever equipped creature kills a creature in combat, put a +1/+1 counter on equipped creature and you gain 3 life.
Equip

Lashed Stones
Artifact (U)
You can't spend to cast Lashed Stones or activate its abilities.
, : Add .

Counting Stones -
Enchantment
At the beginning of each end step, if you control more mountains than the number of Stone counters on ~, put a Stone counter on ~.
Sacrifice ~: ~ deals damage equal to twice the number of Stone counters on it to any target. Activate this ability only if the number of Stone counters on ~ is equal to the number of mountains you control.
Timmy always knew his boulder collection would be useful.

Another concept:

Days of Future Past
Enchantment — Saga
I - Choose 4, 5, or 6. Reveal the card that is that number of cards from the top of your library. If it's a creature card, you may put it onto the battlefield tapped.
II - Target player reveals the top six cards on their library. Choose any number of them and put them into that player's library. That player puts the rest on top in any order.
III - Return a creature you control and a card in your graveyard to their owners' hands.