Fireball

This spell costs {1} more to cast for each target beyond the first.
Fireball deals X damage divided evenly, rounded down, among any number of targets.

The Jolly Balloon Man

Haste
{1}, {T}: Create a token that's a copy of another target creature you control, except it's a 1/1 red Balloon creature in addition to its other colors and types and it has flying and haste. Sacrifice it at the beginning of the next end step. Activate only as a sorcery.

Cadric, Soul Kindler

The "legend rule" doesn't apply to tokens you control.
Whenever another nontoken legendary permanent you control enters, you may pay {1}. If you do, create a token that's a copy of it. That token gains haste. Sacrifice it at the beginning of the next end step.

Mana Echoes

Whenever a creature enters, you may add an amount of {C} equal to the number of creatures you control that share a creature type with it.

Impact Tremors

Whenever a creature you control enters, Impact Tremors deals 1 damage to each opponent.