5 Oct 2018
If any exiled cards you own are face down, they have no characteristics. If they're normally instants or sorceries, they won't be counted.
5 Oct 2018
If a card with jump-start is put into your graveyard during your turn, you'll be able to cast it right away if it's legal to do so, before an opponent can take any actions.
5 Oct 2018
You must still follow any timing restrictions and permissions when casting a spell with jump-start, including those based on the card's type. For instance, you can cast a sorcery using jump-start only when you could normally cast a sorcery.
5 Oct 2018
If an effect allows you to pay an alternative cost rather than a spell's mana cost, you may pay that alternative cost when you jump-start a spell. You'll still discard a card as an additional cost to cast it.
5 Oct 2018
Beacon Bolt is still on the stack while you count your instant and sorcery cards in your graveyard and in exile. It doesn't count itself.
5 Oct 2018
A spell cast using jump-start will always be exiled afterward, whether it resolves, it's countered, or it leaves the stack in some other way.