He was not banned from competitive play, he was banned from OU to Ubers, the tier of the most powerful Pokemon. However it was only banned by a competitive community named Smogon, a community known to be the center of competitive play, because of its great impact on it, however it is technically not official. Many people play by smogon rules but when not playing on Pokemon Showdown, you technically do not need to follow them if you do not want to do so.
The OU tier leader brought up the following points as to why it had to go:
- Aegislash is an extremely effective Pokemon and has very high risk:reward output.
- Aegislash has multiple different sets that are all effective.
- It has numerous sets, most of which are handled differently. If you guess the purpose wrong, you're often losing at least 1 Pokemon
- it introduces literal arbitrary decisions, namely in the form of frequent 50/50s with King's Shield. This is so important because the 50/50 decision IS NOT an even trade for user and opponent, which people seem to be arguing it is. Remember, using King's Shield makes Aegislash have 150 defenses again...meaning the user has the 50/50 as well as 150 defenses. The opponent only has the 50/50. Yes, the user might guess wrong and the opponent "can set up," but this is a specific scenario and dependent on the 50/50, not independent of it.
- Guessing between attacking or not attack Aegislash has determined many high level ladder matches, and there is no skill involved here. It is simple arbitrary guessing. There is no "gaining of information" on the opponent to "best predict" a switch or something...it is literally just "here is a guess, make it, hope for the best." So, Aegislash forces the opponent to guess its set, at the risk of losing a significant member, and forces the opponent to guess an arbitrary 50/50 which is not even, at the risk of again losing a significant member.
OU Tier Leader,Aldaron
On Pokemon Showdown, every person to qualify for the reqs (usually good ladderers) was given the power to vote for its ban. It ended up in Aegislash's disadvantage so it got booted out of the OU tier, but not out of competitive play as it can still be used in Ubers.