Tank Metagross - Never seen this set in play before, and despite what the analysis says I'd much rather use Skarmory for the spikes and phazing aspect, rather than this.
I've actually tested this one a fair amount, and found it to be a pretty good set. I use it as a mid/late game SRer and a check to many of the game's biggest threats, nothing else can boast it's extremely impressive overall defenses, ability to blow up with enough power to KO almost everything in OU, while providing enough of a threat with EQ/MM to prevent it being "setup bait unless you explode" (other than against Skarm/Bronzong), and Stealth Rock.
27.7% - 32.7% from offensive Latias Surf
41.5% - 48.9% from +1 offensive Latias Surf
58.8% - 69.8% ScarfTran Earth Power
92.9% - 110.4% ScarfTran Flamethrower (you don't want to stay in on this, but if a super effective STAB attack off 130 base SpA hitting it's weaker defense has a fair chance to not OHKO, that's saying something)
75.3% - 89% from LO +1 offensive Gyarados Earthquake
80.4% - 95.6% from LO offensive Gyarados Earthquake+Waterfall
71.4% - 84.6% from LO +1 offensive Salamence Earthquake
74.7% - 88.5% from LO offensive Salamence Fire Blast
13.2% - 15.7% CBScizor Bullet Punch
31.3% - 36.8% CBScizor U-turn
22.8% - 26.9% CBtar Stone Edge (what else is going to take Stone Edges like that?)
40.7% - 48.4% DDtar EQ
61% - 72% +1 DDtar EQ
79.1% - 93.4% +1 LO DDtar EQ
As you can see, even the very strongest boosted super effective attacks struggle to KO this set. This gives you time to set up SR on a switch, then beat down your foe or explode. Reliably getting SR up then KOing one foe puts you at a clear advantage, and generally that's what it does (unless you switch in as a huge threat sets up, then you just KO the huge threat which is still pretty nice). Admittedly, they can switch on the explosion. But very little can survive one, and the few that can take huge damage (bar Rotom-A/other ghosts) and since you forced their threat out and get a Pokemon of your choice in against one of their key walls, it's often not a huge problem.
Basically, something can lategame SR better than it. Something can suicidally check the top setup threats better than it. Something can be a bulky offensive wallbreaker better than it. But I don't think anything can provide all of these things at once anywhere like as well.
Can't vouch for the effectiveness of Light Screen, but this set plays very differently from Skarm. Skarm is
far more easily walled than tank gross thanks to Steel/Ground's decent coverage and the difference in attack (212 Vs 306), and lacks Explosion which is one of the main attractions to me. Skarm wants to stick around and wall the big threats while setting up spikes, Metagross wants to switch in, get SR up, then either check things with it's awesome defenses and attacks, or provide a last line of defence against almost anything by surviving what they throw at it and blowing up.
Edit: Also, look at the resistances. Skarm is immune to ground which is awesome, but lacks the Rock/Ice resist and has that ever annoying electric weakness. Which type is better depends on what you're facing.
