Jacecaster Mage (Vryn's Prodigy) and Force of Will

[Fox]

Jace, Vryn's Prodigy
So you flip Origins' Jace and -3 targeting FoW. Since it's not technically flashback, you can skip paying 5 and just exile a blue card and pay 1 life?

[Meekrab]

"You may cast target instant or sorcery card from your graveyard this turn."

Sounds like you can cast it however it allows you to cast it.

[cdr]

Jace, Vryn's Prodigy
So you flip Origins' Jace and -3 targeting FoW. Since it's not technically flashback, you can skip paying 5 and just exile a blue card and pay 1 life?

I guess Jace, Telepath Unbound doesn't work?

Since JTU's effect just says that you can cast the card, you can pay alternate costs to cast it.

Effects like Flashback are structured as alternate costs, and you can only pay one alternate cost (http://www.yawgatog.com/resources/magic-rules/#R1179a) for a spell - so you don't have the option of an alternate cost when using Flashback, just the Flashback cost.

[jrsthethird]

I'm assuming you can also pay alternate costs for Abbot of Keral Keep then too?

[cdr]

Yep. So long as the effect has you playing the card and is not imposing its own alternate cost ala Flashback or "without paying its mana cost" (zero is an alternate cost).

[Fox]

Oh Abbot ought to be fun with Massacre.