You guys realize that Hippo is tanking +2 Shadow Claw from 252 Atk Life Orb Aegislash, right? Hippo is a solid counter, it doesn't matter what set he's running. The best Aegislash can do vs Hippo switchins is to either CB Shadow Claw on the switch, or do the Mix-Set with Life Orb Shadow ball. Swords dance set sits there, potentially gives Hippo a free turn for Stealth Rocks as you King's Shield, and then dies to repeated Earthquakes.
The major issue is that without King's Shield, you have to switch out when anything that threatens you shows up, and a +2 Aegislash even with LO still has a lot of things that it can't OHKO. Which means that if you want to get Aegislash back into the game, you'll have to switch him back in and then boost AGAIN, which will be very difficult to do without King's Shield.
How does losing an attack (and therefore coverage) to King's Shield help you with this situation?
Hippo, or some other bulky water / bulky ground unit is going to switch in while Aegislash stats up, and then forces it out. It doesn't matter if its using King's Shield to block the hit: Aegislash
still loses because Shadow Sneak doesn't do enough damage, and EQ 2HKOs even in Shield form. Icing on the cake: Earthquake is a non-contact move, so King's Shield does NOTHING. In contrast, Hippo welcomes the weaker attacks on King's Shield / SD sets, laughs off all attacks, slacks-off all the damage, sets up Stealth Rocks while you're twiddling your thumbs playing King's Shield games, and then still owns Aegislash no matter what happens. Aegislash is forced to switch out or die when Hippo switches in, no matter what set Aegislash is doing.
Its not just Hippo, its the entire class of bulky waters / bulky grounds that can implement this strategy. Gliscor walls Aegislash. Gyarados walls him. Gastrodon walls him. Old School players can pull out Suicune or Swampert and own him. Any decent wall... hell... Sp. Def Togekiss take the +2 Shadow Sneak / Sacred Sword, laughs at it, and probably wins with Thunderwave / Flinchax. Garchomp can set up and out-Swords Dance the Aegislash due to threatening to OHKO with CB Earthquake. Two attacks are
NOT enough for Aegislash. Worse, many of these threats set up Stealth Rocks... or Dragon Dance (Gyarados) or Swords Dance / Baton Pass (Gliscor). Wasting turns playing King's Shield games opens the door to extremely powerful counter-attacks from the enemy, from a wide variety of threats.
This is NOT the game plan you want, especially not against the better players around here.
Kriptini, you're right. +2 LO Aegislash fails to OHKO a number of threats. Hell, it fails to 2HKO a number of threats. The default mode of Aegislash is to switch in, and then be forced to switch out. Good opponents understand the concept of "pivoting", and against those opponents, you will lose an Aegislash in the best case... and allow a scarrier threat to set up in the worse case. The answer therefore is to find a better set than the Swords Dance / King's Shield set.
Again, UltiMario's Life Orb set however, can threaten Hippo as it runs +Speed EVs, and can hit Shadow-Ball on a predicted switch in. Non Sp. Def Hippos will get 2HKOed before they can attack, but the Sp. Def Hippo is a solid 3HKO. The best chance with the Life Orb set is to Shadow Ball and hope for the Sp. Def lowering luck-hax, and then switch out. If the Life Orb Aegislash player predicts a Slack Off, a risky 2nd Shadow Ball (and more importantly: a 2nd Chance at Sp. Def drop) can potentially destroy the Hippo right here, right now. It relies on luck and out-predicting the opponent. The chance of victory is slim, but is significantly higher than the guaranteed loss than the lulzy King's Shield / SD set that everyone keeps talking about.
The 2nd set that actually does something is the Choice Band set, which honestly deserves more discussion. Aegislash has a 75% chance of 2HKOing Sp. Def Hippowdon with CB Shadow Claw. Each Shadow Claw is a 50% chance for crit, and if either one crits... then Hippowdon is
dead. If the Shadow Claw on the switchin fails to Crit, the CB user is welcome to choose between switching out, or going for the kill. Again, if the CB user predicts the slack-off, he gets another chance for Crit and potentially beats the Hippo.
UltiMario's mixed set, and the CB Set are the two sets for Aegislash. King's Shield / SD is walled by damn near everyone worth talking about, while the Mixed Set and CB Set have extremely hard to deal with options.