The shell itself is mostly unchanged, with a bevy of cheap red removal, blue counterspells, and the iconic 2/1 creature, but there's no consensus on what the best win condition for the deck is. Sometimes you see Madcap Experiment for Platinum Emperion. Sometimes it's Through the Breach and Emrakul, the Aeons Torn. And others just refuse to let the past die, playing Deceiver Exarch and Kiki-Jiki, Mirror Breaker.
The problem with all of these win conditions is that they take up significant deck space while also being poor draws in the early part of the game. You can't stumble in Modern because the decks are too fast and too powerful, and drawing a Platinum Emperion or Emrakul, the Aeons Torn in your opening hand is essentially a mulligan.
So why not play some cheap creatures that are powerful enough to take over a game but leave you with the flexibility to utilize them defensively if need be? Young Pyromancer and Thing in the Ice are great in this role, blocking early creatures, gaining advantage as you cast your cantrips and interactive spells, and applying significant pressure when you decide to turn the corner.
Against aggressive decks they are roadblocks, and against combo decks they let you get a threat down early before you have to leave up countermagic or land a threat in the mid-game without taking your shields down. In control mirrors, they are much easier to resolve and Young Pyromancer especially is difficult to answer with traditional removal, thus forcing your opponent to sideboard awkwardly to answer it.
It seems like the previous versions of this deck tried to get too fancy. Memories of Splinter Twin immediately lead you to want a similar, insta-win kind of play that forces your opponent to constantly worry, but control decks have been successful for decades by simply playing a few powerful creatures. They may not be as flashy, but they get the job done.
Splinter Twin was always a control deck first, rarely assembling a combo on Turn 4 or 5, so it's time to embrace what this shell has always been best at and get back to the basics.