Once I knew Nollan's team was going to be Jellicent + Conkeldurr, I immediately thought of Aegislash, and Mega Pinsir only adds fuel to the fire.
Aegislash @ Leftovers
EVs: 252 HP / 252 SpA / 4 SpD
Quiet Nature
- Shadow Ball
- Flash Cannon
- Substitute
- King's Shield
1 Spe IV
Both Conkeldurr and Mega Pinsir risk King's Shield to attack it and that's only with resisted hits. -2 Mega Pinsir cannot break a Sub in shield form, and Conkeldurr cannot break a Sub even at +0.
Substitute gives Aegislash a way to bypass Jellicent's Will-O-Wisp, and it gels well with Stance Change. Mega Kang's Fake Out helps Aegislash set it up. 1 Spe IV to outspeed Jellicent and Sub before it can WoW, or alternatively Shadow Ball it, which always 2HKOs even accounting for Sitrus Berry.
252+ SpA Aegislash-Blade Shadow Ball vs. 252 HP / 68+ SpD Jellicent: 260-308 (64.3 - 76.2%)
After Jellicent has taken a Shadow Ball and had Sitrus healing, its damage output to Aegislash is not that good: 76 SpA Jellicent Water Spout (90 BP) vs. 252 HP / 4 SpD Aegislash-Blade: 118-141 (36.4 - 43.5%). And that's with a min damage roll from Shadow Ball.
Also:
-Aegislash is immune to Mega Kang's one weakness
-resists all of Cube's weaknesses
-very potent against TR, especially when paired with Mega Kang, which is useful as neither Kang nor Cube enjoy having TR set up