Slip On the Ring

Exile target creature you own, then return it to the battlefield under your control. The Ring tempts you.

Plains

Tawnos Endures

Exile target creature. It gains "At the beginning of your upkeep, if this card is exiled, it perpetually gets +1/+1, then you may put it onto the battlefield."

Resolute Reinforcements

Flash (You may cast this spell any time you could cast an instant.)
When this creature enters, create a 1/1 white Soldier creature token.

Combat Thresher

Prototype {2}{W} — 1/1 (You may cast this spell with different mana cost, color, and size. It keeps its abilities and types.)
Double strike
When Combat Thresher enters, draw a card.

Impassioned Orator

Whenever another creature you control enters, you gain 1 life.

Steel Seraph

Prototype {1}{W}{W} — 3/3 (You may cast this spell with different mana cost, color, and size. It keeps its abilities and types.)
Flying
At the beginning of combat on your turn, target creature you control gains your choice of flying, vigilance, or lifelink until end of turn.

Alabaster Host Intercessor

When Alabaster Host Intercessor enters, exile target creature an opponent controls until Alabaster Host Intercessor leaves the battlefield.
Plainscycling {2} ({2}, Discard this card: Search your library for a Plains card, reveal it, put it into your hand, then shuffle.)

Autonomous Assembler

Prototype {1}{W} — 2/2 (You may cast this spell with different mana cost, color, and size. It keeps its abilities and types.)
Vigilance
{1}, {T}: Put a +1/+1 counter on target Assembly-Worker you control.

Guardian of Ghirapur

Flying
When Guardian of Ghirapur enters, exile up to one other target creature or artifact you control. Return it to the battlefield under its owner's control at the beginning of the next end step.

Lay Down Arms

Exile target creature with mana value less than or equal to the number of Plains you control. Its controller gains 3 life.