Updated the 'Primer' and hopefully explained my really stupid deviations from the usual Twiddle lists.

I can't say this enough but thanks for stopping by!

Hi! I have this deck in paper and I love playing it. How is Sea Gate Stormcaller going for you? It seems very interesting to me.

Also, I’m still not sold on Underworld Breach vs Past in Flames. How had the card fared for you?

Lowenstein,

I've been using Sea Gate Stormcaller in place of Vizier of Tumbling Sands for the most part. At first glance it seems like a 'winmore' but being able to copy a spliced Reach Through Mists or Ideas Unbound. In practice it's basically arcane draw spell 9-11 for me and that's why I dropped Peer Through Depths in an attempt to increase game one resiliency by maining a single Echoing Truth and Eye of Nowhere as well as some Pact of Negations.

As for Underworld Breach, I've always preferred it because with Past in Flames required a bit of twiddle ramping to get it off. Breach only takes one twiddle effect on turn 4 to go off. Also, not really relevant but I liked how convenient it was to tap for red once to get a breach and grapeshot off. That wasn't always the case for me and Past in Flames.

Now I get Underworld Breach has inherent weaknesses because its an enchantment but the ability to drop breach immediately after resolving an arcane draw spell and recycling that same card numerous times in order to win. The escape cost is never an issue since there will naturally be Twiddles & Dream's Grip in the graveyard. Escaping a single copy of a spliced Ideas Unbound twice is more than enough to make sure I don't fizzle.

Lastly, with Underworld Breach the lower CMC also aids with the Sea Gate Stormcaller combo as you'd need to have at 4/5 mana floating to successfully copy a spliced arcane spell. In my limited trials, I found it's a bit difficult to have mana for Past in Flames after that.

Game 2, I always side out Underworld Breach for Aria of Flame and Sea Gate Stormcaller for counterspells / Echoing Truth.

tl;dr Of course it has its own issues but Underworld Breach is pretty consistent for me.

Also, another reason I don't like Past in Flames -

Past in Flames: Only instant and sorcery cards in your graveyard when Past in Flames resolves will gain flashback. Instant and sorcery cards that are put into your graveyard later in the turn, including the resolving Past in Flames, won't gain flashback.