You may exile a red card from your hand rather than pay this spell's mana cost.

Pyrokinesis deals 4 damage divided as you choose among any number of target creatures.

Rulings

Each target must be assigned at least 1 damage.2016-06-08
You divide the damage as you cast Pyrokinesis, not as it resolves. If any of the targets become illegal, damage is dealt to the other targets as originally assigned. If all targets are illegal, Pyrokinesis doesn’t resolve.2016-06-08
If another effect causes Pyrokinesis to cost more, you must pay that additional cost even if you pay its alternative cost.2016-06-08