There is a problem with this. What they can do is Z-EQ to EQ and hope you don't kill, which is most of the time, and the Donphan will win.That's not a nom, just food for thoughts about Victini's viability :
Z-Will-o'wisp is actually a good way to beat Sturdy pokemons (bar Magnezone). The burn status actually prevents most of them from straight up oneshotting you with their Z-move, and the attack boost lets you deal with them once the burn gets rid of sturdy.
252+ Atk burned Donphan Tectonic Rage (180 BP) vs. 144 HP / 0 Def Victini: 306-360 (81.1 - 95.4%) -- guaranteed 2HKO
252+ Atk burned Donphan Continental Crush (200 BP) vs. 144 HP / 0 Def Victini: 226-266 (59.9 - 70.5%) -- guaranteed 2HKO
252+ Atk burned Donphan Ice Shard vs. 144 HP / 0 Def Victini: 11-13 (2.9 - 3.4%) -- possibly the worst move ever
(Ice shard's calcs being there because Priority is nice)
+1 252+ Atk Victini V-create vs. 252 HP / 0 Def Donphan: 345-406 (89.8 - 105.7%) -- 37.5% chance to OHKO after burn damage