Riddle of Lightning

Choose any target. Scry 3, then reveal the top card of your library. Riddle of Lightning deals damage equal to that card's mana value to that permanent or player.

Lightning Phoenix

Flying, haste
Lightning Phoenix can't block.
At the beginning of your end step, if an opponent was dealt 3 or more damage this turn, you may pay {R}. If you do, return Lightning Phoenix from your graveyard to the battlefield.

Ball Lightning

Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
Haste (This creature can attack and {T} as soon as it comes under your control.)
At the beginning of the end step, sacrifice this creature.

Lightning Diadem

Enchant creature
When Lightning Diadem enters, it deals 2 damage to any target.
Enchanted creature gets +2/+2.

Lightning Elemental

Haste (This creature can attack and {T} as soon as it comes under your control.)

Living Lightning

When Living Lightning dies, return target instant or sorcery card from your graveyard to your hand.

Lightning Visionary

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)

Mountain

Weaver of Lightning

Reach (This creature can block creatures with flying.)
Whenever you cast an instant or sorcery spell, Weaver of Lightning deals 1 damage to target creature an opponent controls.

Thriving Bluff

Thriving Bluff enters tapped. As it enters, choose a color other than red.
{T}: Add {R} or one mana of the chosen color.

Lightning-Core Excavator

{5}, {T}, Sacrifice Lightning-Core Excavator: It deals 3 damage to any target.

Lightning Axe

As an additional cost to cast this spell, discard a card or pay {5}.
Lightning Axe deals 5 damage to target creature.

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.