I'm currently something like 5-0 against Grixis delver, which while it's isn't a ginormous sample size, I feel it says at least a little something. Personally, even though it goes counterintuitive to a lot of people's gut reactions, I really really dislike cutting the combo entirely. In addition, by cutting a lot of Twiddlers, you leave them sitting with removal, counters, burn, etc, so when you drop your Thundermaw/Batterskull, it/the token is basically guaranteed to die on sight. 3 Tasigurs will definitely help alleviate that, but I feel like it matches up poorly against a lot of what they have (Delver goes over, Pyro goes wide/will chump, Angler just beats it and Tasis bounce off each other). Your list definitely looks like it plays a bit differently than mine does though. I've been a big fan of trying to slim down and go under them a little bit, because they need to both deploy threats and keep up answers, while for the most part we're able to sit back and just flash things in EOT to pressure their mana.

I'm only 3-2 vs Grixis Delver so I will definitely look to test out your approach. Thundermaw seems hard to resolve and Tasigur matches up poorly. Though they have hard removal, I think it may be manageable without the accompanying hand disruption.

Honestly I really dislike both cutting the combo here as well as your approach to the matchup. In my experience Twin mirrors tend to be won with a little bit more finesse, rather than jamming a bunch of 5 drops in. There've been times where I've drawn a Batterskull on turn 10-11 and had it rot in my hand for another 5-8 turns simply because there's no good opportunity to cast it without suffering a big tempo loss and potentially getting combo'd out. In addition, Thundermaw is also incredibly vulnerable (as is batterskull, to be fair) in that it's very easily tapped down/ignored, and will still take you a few turns to "win". Generally (with a few exceptions), if you connect with a Batterskull in the mirror you're unlikely to lose the "fair" fight. You're also cutting 10 cards and only bringing in 8.

My bad, the extra two cards should be thoughtseize. Updated my previous post to reflect that. Everyone is familiar with the typical route of a control mirror. The passive phase where you are both cantriping and crafting your hands, followed by the phase where you are both throwing haymakers while the other is tapped down. Thoughtseize and Tasigur turn that sort of showdown in our favor rather dramatically. Being able to cast Tasigur for just 1 mana really forces your opponent to act, opening your window to start throwing big punches. With that approach, I would rather have more high impact spells than my opponent. I could see the argument for leaving in your exarchs and some number of splinter twin (in my case it would be 3-1, since I'm only running 3 exarchs) but I think pestermite looks really silly here with bolts and electrolyze floating around.