These calcs show the least defensive EVs possible to guarantee a 3HKO. No AV necessary.
SpD Prioritized:
Without Leftovers, +SpD nature:
252+ SpA Protosynthesis Flutter Mane Shadow Ball vs. 32 HP / 252+ SpD Tinkaton: 135-159 (42.3 - 49.8%) -- guaranteed 3HKO
With Leftovers, +SpD nature:
252+ SpA Protosynthesis Flutter Mane Shadow Ball vs. 0 HP / 212+ SpD Tinkaton: 138-163 (44.3 - 52.4%) -- guaranteed 3HKO after Leftovers recovery
Without Leftovers, neutral nature:
252+ SpA Protosynthesis Flutter Mane Shadow Ball vs. 152 HP / 252 SpD Tinkaton: 147-174 (42.1 - 49.8%) -- guaranteed 3HKO
With Leftovers, neutral nature:
252+ SpA Protosynthesis Flutter Mane Shadow Ball vs. 72 HP / 252 SpD Tinkaton: 147-174 (44.6 - 52.8%) -- guaranteed 3HKO after Leftovers recovery
HP Prioritized:
Without Leftovers, +SpD nature:
252+ SpA Protosynthesis Flutter Mane Shadow Ball vs. 252 HP / 64+ SpD Tinkaton: 157-186 (41.9 - 49.7%) -- guaranteed 3HKO
With Leftovers, +SpD nature:
252+ SpA Protosynthesis Flutter Mane Shadow Ball vs. 252 HP / 4+ SpD Tinkaton: 168-198 (44.9 - 52.9%) -- guaranteed 3HKO after Leftovers recovery
Without Leftovers, neutral nature:
252+ SpA Protosynthesis Flutter Mane Shadow Ball vs. 252 HP / 168 SpD Tinkaton: 157-186 (41.9 - 49.7%) -- guaranteed 3HKO
With Leftovers, neutral nature:
252+ SpA Protosynthesis Flutter Mane Shadow Ball vs. 252 HP / 100 SpD Tinkaton: 168-198 (44.9 - 52.9%) -- guaranteed 3HKO after Leftovers recovery
Hope I helped!