For flygon it doesn't need the speed boost. Because 3 things can happenDirecly from Smogon
Transforms into the target, copying its stats (except HP), moves (at 5 PP each), type, weight, and ability. The stats are copied exactly, without regard to EVs, IVs, and level. IVs of the target are copied for purposes of Hidden Power, as well. Transform copies the target's species, which means that DeapSeaScale, DeepSeaTooth, Light Ball, Metal Powder, Quick Powder, Soul Dew, and Thick Club activate only if the target is the correct species. Level is not copied, so a low level Pokemon does less damage than a high level Pokemon when using the same move (because the attacker's level is part of the damage formula).
Choice Band, Choice Scarf, and Choice Specs keep their boost upon Transforming. The Transforming Pokemon is allowed to select a new move.
If a Pokemon Transforms into Giratina-O, it will instantly revert to the altered forme of Giratina, as it is not holding the Griseous Orb item.
This means that the new ability will not copy your opponents scarf. Unfortunately, this means no revenge killing Scarf-Flygon.
To another note, I am disappointed that it doesn't copy HP, as such we can try to revenge bulky pokemon like CroCune and CurseLax because we cant OHKO them but they can OHKO us.
1. Switch in on EQ, your levitate makes EQ miss. He switches out now but you can use your new U-turn (wich flygon doesn't have U-turn), and take out an appropiate counter.
2. Switch in on outrage, whether transform copies opponents speed with or without choice-scarf your dead anyway.
3. Switch in on U-turn, you get transformed into flygon, take a NVE U-turn and have a scarf-flygon to play with for free, assuming you use scarf ditto.(especially nice if the opponents steels are dead). If you get the choice-scarf boost, great +2 speed flygon, if not. You won't be facing a speed tie due to U-turn.
4. Switch in on flygon using roost/fire-punch/stone-edge ect. All NVE moves, he's locked and you can use his roost to heal your ditto or use another attack for free. (again outrage if his steels are dead).