Shore Up

Target creature you control gets +1/+1 and gains hexproof until end of turn. Untap it. (It can't be the target of spells or abilities your opponents control.)

Festival Crasher

Whenever you cast an instant or sorcery spell, Festival Crasher gets +2/+0 until end of turn.

Lightning Bolt

Lightning Bolt deals 3 damage to any target.

Eroded Canyon

Eroded Canyon enters tapped.
When Eroded Canyon enters, it deals 1 damage to target opponent.
{T}: Add {U} or {R}.

Dive Down

Target creature you control gets +0/+3 and gains hexproof until end of turn. (It can't be the target of spells or abilities your opponents control.)

Accumulated Knowledge

Draw a card, then draw cards equal to the number of cards named Accumulated Knowledge in all graveyards.

Mountain

Tempest Angler

Whenever you cast a noncreature spell, put a +1/+1 counter on Tempest Angler.

Flaring Pain

Damage can't be prevented this turn.
Flashback {R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Barge In

Target attacking creature gets +2/+2 until end of turn. Each attacking non-Human creature gains trample until end of turn.

Chain Lightning

Chain Lightning deals 3 damage to any target. Then that player or that permanent's controller may pay {R}{R}. If the player does, they may copy this spell and may choose a new target for that copy.

Unable to Scream

Enchant creature
Enchanted creature loses all abilities and is a Toy artifact creature with base power and toughness 0/2 in addition to its other types.
As long as enchanted creature is face down, it can't be turned face up.

Consider

Surveil 1. (Look at the top card of your library. You may put it into your graveyard.)
Draw a card.

Titan's Strength

Target creature gets +3/+1 until end of turn. Scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Kindlespark Duo

{T}: Kindlespark Duo deals 1 damage to target opponent.
Whenever you cast a noncreature spell, untap Kindlespark Duo.

Island

Spell Pierce

Counter target noncreature spell unless its controller pays {2}.

Artful Dodge

Target creature can't be blocked this turn.
Flashback {U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)