The Flickers:

Siren's Ruse: We just want it for its flicker effect, seeing as we're not playing pirates. (Sailor of Means was in the deck for a while, but was cut, since you'd rather flicker for a counterspell or removal).
Justiciar's Portal: Same as above, although it's secondary first strike effect does come in handy often as well - spend your Siren's Ruses first for this reason.
These two make all of the below creatures double up as spells

The Menu (actually creatures (but sorta spells)):

Omenspeaker: Great blocker. Scry 2.
Shield Mare: Helps keep you alive against aggro decks - especially if they try to kill it (and then especially if you flicker it). The red unblockable part is only useful occasionally though.
Exclusion Mage: Takes away a big hitter for a turn and also removes their +1/+1 counters. He can remove a token creature, but that job is best saved for Deputy.
Deputy of Detention: His best target is a swarm of tokens, but otherwise he's unconditional removal, so useful for planeswalkers as well. Be wary of detaining creatures with ETB triggers, as you will be flicking this at some point.
Knight of Autumn: Brilliant Jack-of-all-trades. Is mostly used as enchantment-removal, but the life gain is also welcome against aggro decks and late game you reflicker it with 2 +1/+1 counters. If Deputy gets caught by Ixalan’s Binding, you can still use this to free him – and vice versa.
Frilled Mystic: Our flickerable counterspell. Can be a bit hard to mana fix for, but usually isn't a problem. Once it's on the board though it.
Archway Angel: We're playing 12 gates, so this will give you a ton of life if it resolves late game. And when you begin to flicker it, your life total can quickly outreach many opponent's

The Dinner Guest:

Lumbering Battlement “Chompsy”: The star of the deck. Play to make sure you have as many useful (and diverse) ETB effect creatures on the board as possible, then eat them all up with Chompsy. This usually makes him a monster that can block anything. The vigilance makes sure you can ping down one of their creatures each turn - if they have no creatures.. well then...
If you've given Chompsy a diverse diet, then killing him won't help them, as you'll get all your ETB's back to clear him out - and if you manage to interrupt removal with a flicker, then you get to ETB all your creatures and then return them to the safety of Chompsy's belly once more.

The Rest:

Absorb: Just a bit extra against red aggro. Save this for potential board wipers.
Repudiate//Replicate: This card is great. In a pinch you can use Replicate to double up a useful ETB trigger, but it's really the Repudiate part that makes it shine. Counters enemy ETB triggers (especially stuff like Ravenous Chupacabra, if you don't have flickers ready), counters expensive Adapt triggers. Also counters triggers on sagas, which is useful for especially Eldest Reborn and History of Benalia. Very versatile card.
Guild Summit: Seeing as the mana base ended up in gates, might as well include this brilliant card engine. The initial card draw is nice, but if possible try to keep 2 mana open after casting it, to have flickers open still - it'll still more than earn it's keep with incoming gates. The draw from this also lets us cut a few lands from the deck.

The Mana:

Plaza of Harmony: Yes, I know 22 lands seems kinda low, especially with the cost on some of the creatures, and especially playing gates tapped, but this is where Plaza saves the day with it's life gain - it's sorta like half a gift of Paradise, but for free. Also it the “doubling mana type” effect it has with gates makes it much easier to cast Shield Mare and especially Frilled Mystic. Be sure to save these (or a basic land) for when you need to play on curve and the gate setup shouldn't be a problem.
Azorius+Selesny+Simic Guildgates: 4 of each! Basic lands for the rest.

 The Sidedish (only for Best of 3):

Forbidding Spirit: Useful against wide creature decks. And the ability stacks, so if Chompsy regurgitates and eats it several times in a turn, then the enemy will not be attacking.
Wilderness Reclamation: Has been in an out a couple of times, but just ended up being slotted out, dues to not really being necessary very often.
Crafty Cutpurse: I just really want to steal an entire March of the Multitudes. Or the Afterlife remains after a board wipe. Very niche, but could be useful? Also it’s a pirate that could actually be useful with Siren’s Ruse’s second effect.