The short of it is that this deck is real. Deceiver Exarch is a fine card on its own (see also: Modern, the format), and Splinter Twin is a decent way to
not have to play Magic against a subset of Legacy decks. It’s very likely that what this deck wants is a way to out-midrange a removal-heavy deck like BUG
or Maverick that has answers for Splinter Twin and was built to withstand Stoneforge Mystic into Batterskull. In those cases, it’s likely that Elspeth,
Knight-Errant is called for.
The sideboard is too combo-antagonistic, which is a compensation for the fact that the maindeck is so weak to combo. Although Squadron Hawk was cute, I
think that it’s likely just a little too underpowered against the decks featured here. Of course, if you’re playing against Liliana of the Veil and Baleful
Strix all the time, you may feel differently about Hawk. If you cut Hawk and add some interaction — Spell Pierce, Vendilion Clique, whatever — then you
can tailor your sideboard to be a little more midrange-antagonistic instead of relying on Squadron Hawk against decks that can bring in Golgari Charm and
All in all, though, I think that Exarch and Twin provide an excellent third angle to the Mystic + Jace UWx midrange-control decks that have existed in
Legacy for years. If any of you are planning on taking this to a tournament in the near future, do let me know — I’ll be fascinated to see where you take
it. Good luck!