Amphibian Downpour

Flash
Storm (When you cast this spell, copy it for each spell cast before it this turn. You may choose new targets for the copies. Copies become tokens.)
Enchant creature
Enchanted creature loses all abilities and is a blue Frog creature with base power and toughness 1/1.

Llawan, Cephalid Empress

When Llawan enters, return all blue creatures your opponents control to their owners' hands.
Your opponents can't cast blue creature spells.

Indigo Faerie

Flying
{U}: Target permanent becomes blue in addition to its other colors until end of turn.

Sea Kings' Blessing

One or more target creatures become blue until end of turn.

Inundate

Return all nonblue creatures to their owners' hands.

Cerulean Wisps

Target creature becomes blue until end of turn. Untap that creature.
Draw a card.

Neurok Transmuter

{U}: Target creature becomes an artifact in addition to its other types until end of turn.
{U}: Until end of turn, target artifact creature becomes blue and isn't an artifact.

Sapphire Medallion

Blue spells you cast cost {1} less to cast.

Mercurial Transformation

Until end of turn, target nonland permanent loses all abilities and becomes your choice of a blue Frog creature with base power and toughness 1/1 or a blue Octopus creature with base power and toughness 4/4.

Polymorphist's Jest

Until end of turn, each creature target player controls loses all abilities and becomes a blue Frog with base power and toughness 1/1.

Misdirection

You may exile a blue card from your hand rather than pay this spell's mana cost.
Change the target of target spell with a single target.

Kefnet's Monument

Blue creature spells you cast cost {1} less to cast.
Whenever you cast a creature spell, target creature an opponent controls doesn't untap during its controller's next untap step.