I've been enamored with Jace, Cunning Castaway since he was spoiled a couple of days ago. While some people think he may work better in an UGx Simic Merfolk aggro deck of some sort, I think he'd be more fun to play in a pirate deck! The deck I have in mind is designed to exploit every aspect of Castway including ult-ing him creating an army of Jaces:
NOTE: The deck(s) will change periodically as more Ixalan cards are spoiled.
The deck very much plays like an aggro/tempo style. The idea is to play numerous 2cmc pirates with evasion that can get in damage early and trigger Jace, Cunning Castaway's +1 ability and draw into our deck for kill spells to protect him until we can get is ultimate off. The late game relies on pumping our Human Pirates via anthem affects from Admiral Beckett Brass and Vanquisher's Banner hitting for big damage.
Slither Blade: An evasive 1-drop that can't be blocked. Great for triggering Jace's +1. Skyship Plunderer: An evasive 2-drop with flying. It's triggered ability can add a Loyalty to Jace speeding up the clock on getting off his ult. Daring Saboteur: Kinda slow to start, but double the "loot" effect for two cards a turn when paired with Jace's +1. Cartouche of Knowledge: Provides gas via card draw and evasion for creatures that normally lack it. Anointed Procession: Could be considered too "cute" and "win more" but can lock down the game once Jace's ult goes off.
Well, there's the obvious weakness of the deck being 4 colors. I'll be the first to admit that I'm not that best at building mana bases (If anyone knows of a website/program/app I can use to do this for me, please let me know). I'm not even sure if its worth splashing W for Anointed Procession.
This build is more of an "all in" type of strategy, relying less on removing threats and protecting our creatures, and more on being aggressive and making our creatures unblockable. I like this build much more than the 4-Color one for a number of reasons. The mana base is more consistent and it has more ways to bypass blockers, plus it has even more card draw!
It's hard to call a meta that will completely change in a month. However, there is one deck that will lose very little if any power come rotation, and that's Ramunap Red. On paper, Red can theoretically out aggro us because it has many creatures with haste that also grant unblockability when they enter the battlefield. It also plays a 1 and 2 drop removal spells that easily kill all our guys. The best hope we have of winning the match-up is post board when we can add in more counter spells.
Just as an aside, Temmet's ability kills Jace's tokens, and Ragavan isn't around when the ability triggers.
That said, the plan for Skyship Plunderer into Jace is extremely strong, and the main feature worth exploiting into a powerful turn 4 either via Admiral Beckett Brass, or that 2UU Flash pirate siren.
Temmet's triggered ability works just fine on Jace's tokens because it isn't a spell targeting said token, but an ability. But you're right about it not working on Ragavan token because it happens before attacks are declared.
I like Dreamcaller Siren but I can't figure out (yet) where or if it slots in. In my 4c or Grixis build, maybe. In my Jeskai build, probably not.
EDIT: Added Dreamcaller Siren to my Jeskai build. Really like how its testing and have completely abandoned to 4-Color build entirely.