I vote ban for shadow tag ability.
When your opponent is using gothitele, even if u have a revenge killer for it, they tend to have a support for gothitele to prevent it dies.( supports eg. conkeldurr, poliwarth etc..)
When your sand team vs ur opponent's sand team, Gothitelle can kill your tangorwth with signal beam and your opponent's excadrill will easily sweep your entire team .
Additionally, gothitelle can set up calm mind and win in pp war against stall pokemons like blissey..
We have no choice when our pokes are trapped except disconnecting.