How does a jolly meg sceptile w/ SD compare to a special attack based one?
252 Atk Mega Sceptile Leaf Blade vs. 0 HP / 0 Def Mew: 132-156 (38.7 - 45.7%) -- guaranteed 3HKO
252 SpA Mega Sceptile Leaf Storm vs. 0 HP / 0 SpD Mew: 229-271 (67.1 - 79.4%) -- guaranteed 2HKO
+2 252 Atk Mega Sceptile Leaf Blade vs. 0 HP / 0 Def Mew: 262-309 (76.8 - 90.6%) -- guaranteed 2HKO
Much the same way as SD Sceptile compares to special Sceptile: after a Swords Dance, it is in fact more powerful. However, until it actually gets a chance to use Swords Dance, its quite a bit weaker initially. Lightningrod boosts are a bit easier to nab in general, since things like Thundurus hardly ever think twice about clicking the "lol Prankster Dick Wave" button. Both have downsides, of course: Sceptile is scared shitless of T-Wave until it Megas, meaning it can't switch in to T-Waves until you get a clean switch to Mega. With SD, you need to come in on something that can't tickle you (keep in mind that Ice Beam/HP Ice/Ice Punch can be run on a TON of stuff), and set up on the switch out. +2 Low Kick can actually, you know, hit things, and is actually reasonable to 2HKO something like Mega Khan with (unlike Focus Blast). Also:
+2 252 Atk Mega Sceptile Low Kick (120 BP) vs. 252 HP / 0 Def Heatran: 442-522 (114.5 - 135.2%) -- guaranteed OHKO
252 SpA Mega Sceptile Focus Blast vs. 252 HP / 4 SpD Heatran: 270-318 (69.9 - 82.3%) -- guaranteed 2HKO
Have fun with those Focus Blast coinflips and predicting the switchin. I will be fair though:
+1 252 SpA Mega Sceptile Focus Blast vs. 252 HP / 4 SpD Heatran: 404-476 (104.6 - 123.3%) -- guaranteed OHKO
rather poorly, base 110 attack compared to 145 sp attack so you have less damage, coverage is less optimal than special attacking one. Issues with 4 move syndrome where you have to sacrifice something to be able to something else. Oh and lightning rod raises it's sp attack when hit with electric type attacks.
-1 252 Atk Mega Sceptile Outrage vs. 0 HP/0 Def Mega Salamence: 102 - 120 (60 - 70.6%) -- guaranteed 2HKO
252 SpAtk Mega Sceptile Dragon Pulse vs. 0 HP/0 SpDef Mega Salamence: 170 - 204 (100 - 120%) -- guaranteed OHKO
Not if you get an SD in on a previous mon or the switchin. Special Mega Sceptile is more reliable on a MegaMence KO, though, yes, as it needs no setup at all.
+1 252 Atk Mega Sceptile Outrage vs. 0 HP / 4 Def Mega Salamence: 416-492 (125.6 - 148.6%) -- guaranteed OHKO
As for less optimal coverage, I feel like I'm missing something. All it misses is Ice and... I don't think Sceptile runs HP Ice (does it?).
Grass (Leaf Storm, Energy Ball, Solarbeam, Giga Drain | Leaf Blade)
Fighting (Focus Miss | Low Kick, Drain Punch, Focus Punch)
Dragon (Dragon Pulse | Dragon Claw, Dual Chop, Outrage)
Ground (HP Ground | Earthquake)
Rock (HP Rock | Rock Slide)
Ice (HP Ice | Nothing)
Electric (HP Electric | Thunderpunch)
tl;dr:
Physical sucks without a hard to obtain SD boost, but hits pretty hard after it with accurate coverage and no negative side effects, with a decent array of coverage moves to pick from alongside its STABs - but loses a move slot to Swords Dance. Special is more reliable, thanks to not being total shit without a boost, doesn't lose a moveslot to Lightningrod, and can bait Electric moves for a free boost - but only after it gets a free Mega turn. It also relies on Leaf Storm to do any real damage thanks to the shit power of Giga Drain and Dragon Pulse, so its going to switch out a lot and lose LR boosts doing so. Also, Focus Blast is shit, the actual odds of 2HKOing something like Ferrothorn or Heatran will kill you more often than not and its not like it has anything except a second Grass move or Hidden Power if you opt out of Focus Blast. Discharge shenanigans could be funny in doubles, but Sceptile's pretty easy to kill. Also, Talonflame.
So imo, it's a "Pick your poison, can't really go
too wrong either way". SD sweeps in the right conditions, Special does hit and run a hell of a lot better and is a better revenge killer, but doesn't have the same long-term damage potential because Leaf Storm.