Scion of Vitu-Ghazi

When Scion of Vitu-Ghazi enters, if you cast it from your hand, create a 1/1 white Bird creature token with flying, then populate. (Create a token that's a copy of a creature token you control.)

Securitron Squadron

Squad {3} (As an additional cost to cast this spell, you may pay {3} any number of times. When this creature enters, create that many tokens that are copies of it.)
Vigilance
Whenever a creature token you control enters, put a +1/+1 counter on it.

Radiant, Serra Archangel

Flying
Tap another untapped creature you control with flying: Radiant, Serra Archangel gains protection from the color of your choice until end of turn.
Partner (You can have two commanders if both have partner.)

Staff of the Storyteller

When Staff of the Storyteller enters, 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.

Scholar of New Horizons

Scholar of New Horizons enters with a +1/+1 counter on it.
{T}, Remove a counter from a permanent you control: Search your library for a Plains card and reveal it. If an opponent controls more lands than you, you may put that card onto the battlefield tapped. If you don't put the card onto the battlefield, put it into your hand. Then shuffle.

Sephara, Sky's Blade

You may pay {W} and tap four untapped creatures you control with flying rather than pay this spell's mana cost.
Flying, lifelink
Other creatures you control with flying have indestructible. (Damage and effects that say "destroy" don't destroy them.)

Katerina of Myra's Marvels

As Katerina of Myra's Marvels enters, 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.)

Sanctifier of Souls

Whenever another creature you control enters, Sanctifier of Souls gets +1/+1 until end of turn.
{2}{W}, Exile a creature card from your graveyard: Create a 1/1 white Spirit creature token with flying.

Sisay's Ring

Star Compass

Star Compass enters tapped.
{T}: Add one mana of any color that a basic land you control could produce.

Serra Redeemer

Flying
Whenever another creature you control with power 2 or less enters, put two +1/+1 counters on that creature.

Symmetry Matrix

Whenever a creature you control with power equal to its toughness enters, you may pay {1}. If you do, draw a card.

Sol Talisman

Suspend 3—{1} (Rather than cast this card from your hand, pay {1} and exile it with three time counters on it. At the beginning of your upkeep, remove a time counter. When the last is removed, you may cast it without paying its mana cost.)
{T}: Add {C}{C}.

Shire Shirriff

Vigilance
When Shire Shirriff enters, you may sacrifice a token. When you do, exile target creature an opponent controls until Shire Shirriff leaves the battlefield.

Sol Ring

Stonespeaker Crystal

{T}: Add {C}{C}.
{2}, {T}, Sacrifice Stonespeaker Crystal: Exile any number of target players' graveyards. Draw a card.