Theros

Dissolve | Instant | | Counter target spell. Scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.) | Wesley Burt

Gainsay | Instant | | Counter target blue spell. | Clint Cearley

Horizon Scholar | Creature | Sphinx | Flying When Horizon Scholar enters the battlefield, 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.) | Karl Kopinski

Ordeal of Thassa | Enchantment | Aura | Enchant creature Whenever enchanted creature attacks, put a +1/+1 counter on it. Then if it has three or more +1/+1 counters on it, sacrifice Ordeal of Thassa. When you sacrifice Ordeal of Thassa, draw two cards. | Howard Lyon

Sea God's Revenge | Sorcery | | Return up to three target creatures your opponents control to their owners' hands. Scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.) | Eric Velhagen

Sealock Monster | Creature | Octopus | Sealock Monster can't attack unless defending player controls an Island. {5}{U}{U}: Monstrosity 3. (If this creature isn't monstrous, put three +1/+1 counters on it and it becomes monstrous.) When Sealock Monster becomes monstrous, target land becomes an Island in addition to its other types. | Adam Paquette

Thassa's Emissary | Enchantment Creature | Crab | Bestow {5}{U} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.) Whenever Thassa's Emissary or enchanted creature deals combat damage to a player, draw a card. Enchanted creature gets +3/+3. | Sam Burley

Triton Fortune Hunter | Creature | Merfolk Soldier | Heroic — Whenever you cast a spell that targets Triton Fortune Hunter, draw a card. | Clint Cearley

Triton Tactics | Instant | | Up to two target creatures each get +0/+3 until end of turn. Untap those creatures. At this turn's next end of combat, tap each creature that was blocked by one of those creatures this turn and it doesn't untap during its controller's next untap step. | Jack Wang

Battlewise Hoplite | Creature | Human Soldier | Heroic — Whenever you cast a spell that targets Battlewise Hoplite, put a +1/+1 counter on Battlewise Hoplite, then scry 1. (To scry 1, look at the top card of your library, then you may put that card on the bottom of your library.) | Willian Murai

Shipwreck Singer | Creature | Siren | Flying {1}{U}: Target creature an opponent controls attacks this turn if able. {1}{B}, {T}: Attacking creatures get -1/-1 until end of turn. | Daarken

Spellheart Chimera | Creature | Chimera | Flying, trample Spellheart Chimera's power is equal to the number of instant and sorcery cards in your graveyard. | Svetlin Velinov

Horizon Chimera | Creature | Chimera | Flash Flying, trample Whenever you draw a card, you gain 1 life. | Sam Burley