hp ground is quite rare on musharna anyway, because having no signal beam makes it harder for musharna to come out on top if it faces another calm mind psychic-type. skuntank is still a good way to keep musharna from muscling its way through teams, but a well-built team will have many ways to dispose of skuntank, like piloswine or sawsbuck.
offensive teams have plenty of other methods to keep musharna from getting away with a sweep; the key here is to carry several ways to check it. some stuff i've been using are rotom-a for trick, and metang, which has a 4x resistance to psychic-type attacks and can toxic in return without fear of synchronize. i've also been messing around with a combination of psychic- and/or ghost-types that people have mentioned in this thread earlier. destiny bond haunter and gardevoir are neat because they can lure musharna or dark-types and get rid of them to free the way for another psychic-type to set up. aside from using toxic for non-heal bell variants of musharna, taunt is also a very interesting option, but it's really hard to fit on many pokemon. misdreavus can use taunt, but that means it can't really switch in to something like alomomola without risking a toxic. samurott is actually one of the best options for a taunt user, having excellent coverage and power in just three attacks to make it a potent wallbreaker. between those support options, as well as having hard-hitting pokemon, most teams usually have few problems with musharna if played well.
if you're using a bulkier team, there's still stuff like bastiodon to take attacks and use roar on any musharna trying to set up. stall teams will usually also have toxic spikes or toxic users that can wear down musharna over the course of the match, even if it has access to heal bell.
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