Shadow of the Second Sun

Enchant player
At the beginning of each of enchanted player's postcombat main phases, there is an additional beginning phase after this phase. (The end step happens after the added untap, upkeep, and draw steps.)

Unbender Tine

Seedborn Muse

Untap all permanents you control during each other player's untap step.

Tidal Force

At the beginning of each upkeep, you may tap or untap target permanent.

Xolatoyac, the Smiling Flood

Whenever Xolatoyac enters or attacks, put a flood counter on target land. That land is an Island in addition to its other types for as long as it has a flood counter on it.
At the beginning of your end step, untap each permanent you control with a counter on it.

Derevi, Empyrial Tactician

Flying
When Derevi enters and whenever a creature you control deals combat damage to a player, you may tap or untap target permanent.
{1}{G}{W}{U}: Put Derevi onto the battlefield from the command zone.

Voltaic Servant

At the beginning of your end step, untap target artifact.

Sphinx of the Second Sun

Flying
At the beginning of each of your postcombat main phases, there is an additional beginning phase after this phase. (The beginning phase includes the untap, upkeep, and draw steps.)

Lita, Mechanical Engineer

Vigilance
At the beginning of your end step, untap each other artifact creature you control.
{3}{W}, {T}: Create a 5/5 colorless Vehicle artifact token named Zeppelin with flying and crew 3. (It has "Tap any number of creatures you control with total power 3 or more: This token becomes an artifact creature until end of turn.")

Unstoppable Plan

At the beginning of your end step, untap all nonland permanents you control.

Unwinding Clock

Untap all artifacts you control during each other player's untap step.

Dramatic Reversal

Untap all nonland permanents you control.

Tezzeret the Seeker

+1: Untap up to two target artifacts.
−X: Search your library for an artifact card with mana value X or less, put it onto the battlefield, then shuffle.
−5: Artifacts you control become artifact creatures with base power and toughness 5/5 until end of turn.

Turnabout

Choose artifact, creature, or land. Tap all untapped permanents of the chosen type target player controls, or untap all tapped permanents of that type that player controls.

Blinkmoth Infusion

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)
Untap all artifacts.