msem-instigator

As Straw Simulacrum enters, choose a creature type.
Straw Simulacrum is the chosen creature type in addition to its other types.
Other creatures you control of the chosen type get +1/+1.

Whenever another creature you control enters, put your choice of a +1/+1 counter, a trample counter, or a haste counter on it.

Stray Sighthound can't be blocked by creatures with power 2 or less.
Attain {3}{G} ({3}{G}: Transform this. Spend at least three colors of mana to activate this, and only as a sorcery.)

Each player chooses one card in their hand, then discards the rest.

When Strayseeker Ranger enters, search your library for a creature card with mana value 2 or less, reveal it, put it into your hand, then shuffle.
Recite {W}{W} (You may cast this creature from your graveyard for its recite cost. If you do, exile it when it enters or if it would leave the battlefield.)

Target player gains X life.

Return target creature to its owner's hand.
Draw a card.

Creatures your opponents control get -3/-0 until end of turn.
Draw a card.

Street Busker gets +2/+0 as long as you've gained life this turn.

At the beginning of your end step, if you control two or more tapped creatures, exile the top card of your library. Until the end of your next turn, you may play that card.

Wither (This deals damage to creatures in the form of -1/-1 counters.)

When Street Performer enters, create a 2/1 blue Illusion creature token with “When this creature becomes the target of a spell or ability, sacrifice it.”

Menace
Deploy 4 (As this enters, you may tap any number of other creatures you control with total power 4 or more.)
When Street Raider enters deployed, discard your hand, then draw three cards.

Enchant creature
Enchanted creature gets +1/+0 and can't be blocked by creatures with greater mana values.

When Street Stalker enters, target opponent loses 1 life for each creature you control named Street Stalker.

Whenever you make first contact, target creature you control can't be blocked by Humans this turn. (You make first contact the first time each turn you cast a spell with a name not in your graveyard or control already.)

At the beginning of your upkeep, return target creature or enchantment card with mana value 2 or less from your graveyard to the battlefield.
At the beginning of your end step, you may sacrifice a creature or enchantment. If you do, draw a card.

Harmony — Target creature gains haste until end of turn.
When Streetside Entertainer enters, harmonize. (Trigger up to one harmony of one permanent you control.)

Ward {1}
Streetslipper can't be blocked.
Whenever you foretell a card or cast a foretold spell, put a +1/+1 counter on Streetslipper.

Improve {1} ({1}: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
At the beginning of combat on your turn, target creature you control with mana value 3 or less can't be blocked this turn. If Streetwise Investigator has two or more counters on it, that creature gains vigilance until end of turn.

Scry 3, then reveal the top card of your library. Target creature gains trample and gets +X/+X until end of turn, where X is that card's mana value.

Enchant creature
When Strength in Imagining enters, if it enchants a face-down creature, put a +1/+1 counter on that creature.
Enchanted creature has flying and trample.

Choose one or both —
• Audition for green. (Create a 1/1 Construct Actor creature token, a Scout Role giving 2/3 and vigilance, or a Warrior Role giving 3/2 and trample. Roles replace older ones.)
• Target creature you control fights target creature you don't control.

Target creature gains hexproof and indestructible until end of turn. If it's legendary, put a +1/+1 counter on it.