Karfell Harbinger

{T}: Add {U}. Spend this mana only to foretell a card from your hand or cast an instant or sorcery spell.

Chronatog Totem

{T}: Add {U}.
{1}{U}: Chronatog Totem becomes a 1/2 blue Atog artifact creature until end of turn.
{0}: Chronatog Totem gets +3/+3 until end of turn. You skip your next turn. Activate only once each turn and only if Chronatog Totem is a creature.

Lapis Orb of Dragonkind

{T}: Add {U}. When you spend this mana to cast a Dragon creature spell, scry 2. (Look at the top two cards of your library, then put any number of them on the bottom of your library and the rest on top in any order.)

Sea Scryer

Alexi, Zephyr Mage

{X}{U}, {T}, Discard two cards: Return X target creatures to their owners' hands.

Unblinking Observer

{T}: Add {U}. Spend this mana only to pay a disturb cost or cast an instant or sorcery spell.

Eye of Ramos

{T}: Add {U}.
Sacrifice Eye of Ramos: Add {U}.

Midnight Clock

{T}: Add {U}.
{2}{U}: Put an hour counter on Midnight Clock.
At the beginning of each upkeep, put an hour counter on Midnight Clock.
When the twelfth hour counter is put on Midnight Clock, shuffle your hand and graveyard into your library, then draw seven cards. Exile Midnight Clock.

Volshe Tideturner

{T}: Add {U}. Spend this mana only to cast an instant or sorcery spell or a kicked spell.

Silver Myr

Sky Diamond

Sky Diamond enters the battlefield tapped.
{T}: Add {U}.

Blue Mana Battery

{2}, {T}: Put a charge counter on Blue Mana Battery.
{T}, Remove any number of charge counters from Blue Mana Battery: Add {U}, then add an additional {U} for each charge counter removed this way.

Machine God's Effigy

You may have Machine God's Effigy enter the battlefield as a copy of any creature on the battlefield, except it's an artifact and it has "{T}: Add {U}." (It's not a creature.)
{T}: Add {U}.