Staff of the Letter Magus

As Staff of the Letter Magus enters the battlefield, choose a consonant other than N, R, S, or T.
Whenever a player casts a spell, you gain 1 life for each time the chosen letter appears in that spell's name.

Soul-Strike Technique

Enchant creature
Enchanted creature gets +1/+1 and has vigilance.
When enchanted creature dies, manifest the top card of your library. (Put it onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card.)

Soul Warden

Whenever another creature enters the battlefield, you gain 1 life.

Silver-Inlaid Dagger

Equipped creature gets +2/+0.
As long as equipped creature is a Human, it gets an additional +1/+0.
Equip {2}

Skyhunter Prowler

Flying, vigilance (This creature can't be blocked except by creatures with flying or reach, and attacking doesn't cause this creature to tap.)

Secure the Wastes

Create X 1/1 white Warrior creature tokens.

Skyhunter Patrol

Flying, first strike (This creature can't be blocked except by creatures with flying or reach, and it deals combat damage before creatures without first strike.)

Sigil of Distinction

Sigil of Distinction enters the battlefield with X charge counters on it.
Equipped creature gets +1/+1 for each charge counter on Sigil of Distinction.
Equip—Remove a charge counter from Sigil of Distinction.

Swiftfoot Boots

Equipped creature has hexproof and haste. (It can't be the target of spells or abilities your opponents control.)
Equip {1}

Nocturno of Myra's Marvels

As Nocturno of Myra's Marvels enters the battlefield, choose a word with five or more letters.
Whenever you cast a spell with the chosen word in its rules text, you draw a card and you lose 2 life.
Partner (You can have two commanders if both have partner.)

Sejiri Glacier

Sejiri Glacier enters the battlefield tapped.
{T}: Add {W}.

Sejiri Shelter

Target creature you control gains protection from the color of your choice until end of turn.

Sejiri Shelter // Sejiri Glacier

Storm Herd

Create X 1/1 white Pegasus creature tokens with flying, where X is your life total.

Siege Veteran

At the beginning of combat on your turn, put a +1/+1 counter on target creature you control.
Whenever another nontoken Soldier you control dies, create a 1/1 colorless Soldier artifact creature token.

Plains

Song of the Worldsoul

Whenever you cast a spell, populate. (Create a token that's a copy of a creature token you control.)

Sigarda's Aid

You may cast Aura and Equipment spells as though they had flash.
Whenever an Equipment enters the battlefield under your control, you may attach it to target creature you control.

Stalking Leonin

When Stalking Leonin enters the battlefield, secretly choose an opponent.
Reveal the player you chose: Exile target creature that's attacking you if it's controlled by the chosen player. Activate only once.

Secret Rendezvous

You and target opponent each draw three cards.

Swords to Plowshares

Exile target creature. Its controller gains life equal to its power.

Scythe of the Wretched

Equipped creature gets +2/+2.
Whenever a creature dealt damage by equipped creature this turn dies, return that card to the battlefield under your control. Attach Scythe of the Wretched to that creature.
Equip {4}

Sacred Cat

Lifelink
Embalm {W} ({W}, Exile this card from your graveyard: Create a token that's a copy of it, except it's a white Zombie Cat with no mana cost. Embalm only as a sorcery.)

Shield of the Avatar

If a source would deal damage to equipped creature, prevent X of that damage, where X is the number of creatures you control.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

Smuggler's Share

At the beginning of each end step, draw a card for each opponent who drew two or more cards this turn, then create a Treasure token for each opponent who had two or more lands enter the battlefield under their control this turn.

Space Marine Scout

First strike, vigilance
Concealed Position — When Space Marine Scout enters the battlefield, if an opponent controls more lands than you, you may search your library for a Plains card, put it onto the battlefield tapped, then shuffle.

Solaflora, Intergalactic Icon

Auras and Equipment you control attached to Solaflora, Intergalactic Icon affect other creatures you control as though those Auras and Equipment were attached to them.
Counters and stickers on Solaflora affect other creatures you control as though those counters and stickers were on them.

Stone Haven Outfitter

Equipped creatures you control get +1/+1.
Whenever an equipped creature you control dies, draw a card.

Soul's Attendant

Whenever another creature enters the battlefield, you may gain 1 life.

Spirited Companion

When Spirited Companion enters the battlefield, draw a card.

Strength-Testing Hammer

Whenever equipped creature attacks, roll a six-sided die. That creature gets +X/+0 until end of turn, where X is the result. Then if it has the greatest power or is tied for greatest power among creatures on the battlefield, draw a card.
Equip {3}

Serra's Embrace

Enchant creature
Enchanted creature gets +2/+2 and has flying and vigilance.

Sorcerer's Wand

Equipped creature has "{T}: This creature deals 1 damage to target player or planeswalker. If this creature is a Wizard, it deals 2 damage instead."
Equip {3}

Serra's Boon

Enchant creature
Enchanted creature gets +1/+2 as long as it's white. Otherwise, it gets -2/-1.

Stasis Snare

Flash (You may cast this spell any time you could cast an instant.)
When Stasis Snare enters the battlefield, exile target creature an opponent controls until Stasis Snare leaves the battlefield. (That creature returns under its owner's control.)

Sublime Exhalation

Undaunted (This spell costs {1} less to cast for each opponent.)
Destroy all creatures.

Sigiled Sword of Valeron

Equipped creature gets +2/+0, has vigilance, and is a Knight in addition to its other types.
Whenever equipped creature attacks, create a 2/2 white Knight creature token with vigilance that's attacking.
Equip {3}

Slagwurm Armor

Equipped creature gets +0/+6.
Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery. This card enters the battlefield unattached and stays on the battlefield if the creature leaves.)

Staff of the Sun Magus

Whenever you cast a white spell or a Plains enters the battlefield under your control, you gain 1 life.

Seraphic Greatsword

Equipped creature gets +2/+2.
Whenever equipped creature attacks the player with the most life or tied for most life, create a 4/4 white Angel creature token with flying that's tapped and attacking that player.
Equip {4}

Sword of the Animist

Equipped creature gets +1/+1.
Whenever equipped creature attacks, you may search your library for a basic land card, put it onto the battlefield tapped, then shuffle.
Equip {2}

Salvage Scout

{W}, Sacrifice Salvage Scout: Return target artifact card from your graveyard to your hand.

Spectral Steel

Enchant creature
Enchanted creature gets +2/+2.
{1}{W}, Exile Spectral Steel from your graveyard: Return another target Aura or Equipment card from your graveyard to your hand.

Stoneforge Masterwork

Equipped creature gets +1/+1 for each other creature you control that shares a creature type with it.
Equip {2}

Spidersilk Net

Equipped creature gets +0/+2 and has reach. (It can block creatures with flying.)
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

Serra's Blessing

Creatures you control have vigilance. (Attacking doesn't cause them to tap.)

Sigil of Valor

Whenever equipped creature attacks alone, it gets +1/+1 until end of turn for each other creature you control.
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Short Sword

Equipped creature gets +1/+1.
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Suspension Field

When Suspension Field enters the battlefield, you may exile target creature with toughness 3 or greater until Suspension Field leaves the battlefield. (That creature returns under its owner's control.)

Skullclamp

Equipped creature gets +1/-1.
Whenever equipped creature dies, draw two cards.
Equip {1}

Samite Blessing

Enchant creature
Enchanted creature has "{T}: The next time a source of your choice would deal damage to target creature this turn, prevent that damage."

Savannah Lions

Staff of the Storyteller

When Staff of the Storyteller enters the battlefield, create a 1/1 white Spirit creature token with flying.
Whenever you create one or more creature tokens, put a story counter on Staff of the Storyteller.
{W}, {T}, Remove a story counter from Staff of the Storyteller: Draw a card.

Skyhunter Cub

As long as Skyhunter Cub is equipped, it gets +1/+1 and has flying.

Slayer's Plate

Equipped creature gets +4/+2.
Whenever equipped creature dies, if it was a Human, create a 1/1 white Spirit creature token with flying.
Equip {3}

Secure the Scene

Exile target nonland permanent. Its controller creates a 1/1 white Soldier creature token.

Katerina of Myra's Marvels

As Katerina of Myra's Marvels enters the battlefield, choose a letter.
Whenever you cast a spell whose name begins with the chosen letter, create a white 2/2 Cat creature token with flying.
Partner (You can have two commanders if they both have partner.)

Sculpted Sunburst

Choose a creature you control, then each opponent chooses a creature they control with equal or lesser power. If you chose a creature this way, exile each creature not chosen by any player this way.

Skyhunter Skirmisher

Seal from Existence

Ward {3} (Whenever this enchantment becomes the target of a spell or ability an opponent controls, counter it unless that player pays {3}.)
When Seal from Existence enters the battlefield, exile target nonland permanent an opponent controls until Seal from Existence leaves the battlefield.

Sanctified Charge

Creatures you control get +2/+1 until end of turn. White creatures you control also gain first strike until end of turn. (They deal combat damage before creatures without first strike.)

Servo Exhibition

Create two 1/1 colorless Servo artifact creature tokens.

Sanctuary Cat

Sram, Senior Edificer

Whenever you cast an Aura, Equipment, or Vehicle spell, draw a card.

Soul Snare

{W}, Sacrifice Soul Snare: Exile target creature that's attacking you or a planeswalker you control.

Savannah Sage

When Savannah Sage enters the battlefield, you gain 2 life.

Skrelv's Hive

At the beginning of your upkeep, you lose 1 life and create a 1/1 colorless Phyrexian Mite artifact creature token with toxic 1 and "This creature can't block."
Corrupted — As long as an opponent has three or more poison counters, creatures you control with toxic have lifelink.

Stroke of Midnight

Destroy target nonland permanent. Its controller creates a 1/1 white Human creature token.

Skeleton Key

Equipped creature has skulk. (It can't be blocked by creatures with greater power.)
Whenever equipped creature deals combat damage to a player, you may draw a card. If you do, discard a card.
Equip {2}

Sceptre of Eternal Glory

{T}: Add one mana of any color.
{T}: Add three mana of any one color. Activate only if you control three or more lands with the same name.

Shuriken

Equipped creature has "{T}, Unattach Shuriken: Shuriken deals 2 damage to target creature. That creature's controller gains control of Shuriken unless it was unattached from a Ninja."
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

Static Net

When Static Net enters the battlefield, exile target nonland permanent an opponent controls until Static Net leaves the battlefield.
When Static Net enters the battlefield, you gain 2 life and create a tapped Powerstone token. (It's an artifact with "{T}: Add {C}. This mana can't be spent to cast a nonartifact spell.")

Scouting Hawk

Flying
Keen Sight — When Scouting Hawk enters the battlefield, if an opponent controls more lands than you, search your library for a basic Plains card, put it onto the battlefield tapped, then shuffle.

Sword of Hours

Whenever equipped creature attacks, put a +1/+1 counter on it.
Whenever equipped creature deals combat damage, roll a d12. If the result is greater than the damage dealt or the result is 12, double the number of +1/+1 counters on that creature.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

Skyhunter Strike Force

Flying
Melee (Whenever this creature attacks, it gets +1/+1 until end of turn for each opponent you attacked this combat.)
Lieutenant — As long as you control your commander, other creatures you control have melee.