Interesting Build, but as far as a Tyrantrum, I was looking at this build:
Tyrantrum @ Assault Vest
Ability: Strong Jaw
EVs: 252HP / 4 Def / 252 SpD
Adamant Nature
- Rock Tomb
- Dragon Claw
- Poison Fang
- Ice Fang
Allow me to post these Calculations:
I like these Numbers, and I have the perfect supporter who can cast screens and Sandstorm.
This Tyrantrum set isn't worth it as I already mentioned. You're wasting away Tyrantrum's niche of recoil-free Head Smashes. Even with Strong Jaw, Poison Fang still does less damage to Fairies than a neutral Head Smash. Fire Fang is only good against Ferrothorn and Scizor, while Ice Fang is redundant with Tyrantrum's Dragon STAB. While Rock Tomb can slow down opponents, it's not good as a main STAB attack because of its low base power, and Tyrantrum can fix its average Speed with Dragon Dance or Rock Polish anyway. The heavy specially defensive investment also makes Tyrantrum sorely miss out on plenty of power.
Calcs to prove my point about Poison Fang (and this is for 0 Attack investment, and max Attack investment, respectively, with a neutral nature):
0 Atk Strong Jaw Tyrantrum Poison Fang vs. 244 HP / 0 Def Sylveon: 94-112 (46.7 - 55.7%) -- 70.7% chance to 2HKO
0 Atk Tyrantrum Head Smash vs. 244 HP / 0 Def Sylveon: 141-166 (70.1 - 82.5%) -- guaranteed 2HKO
252 Atk Strong Jaw Tyrantrum Poison Fang vs. 244 HP / 0 Def Sylveon: 116-138 (57.7 - 68.6%) -- guaranteed 2HKO
252 Atk Tyrantrum Head Smash vs. 244 HP / 0 Def Sylveon: 172-204 (85.5 - 101.4%) -- 12.5% chance to OHKO
Assault Vest is for those Pokemon who have some of the following: good HP and/or Special Defense, defensive utility that doesn't come from status moves, and defensive typing. Tyrantrum doesn't really fulfill any of these. Here are some better Assault Vest users and why they're generally better users of said item than Tyrantrum:
-Conkeldurr has good physical bulk, but its low Special Defense makes it susceptible to special attacks. Assault Vest allows it to patch up this weakness. It also has offensive recovery in Drain Punch.
-Azumarill has a good defensive typing in Water/Fairy, and decent bulk all-round, and pretty much the only status move it uses is Belly Drum, but that's a different story.
-Therian Tornadus may have sweeper-oriented stats, but it has the Regenerator ability to compensate for its lack of recovery moves.
https://www.smogon.com/smog/issue35/assault-vest This article should go more in-depth on what (not) to use Assault Vest on.