The team is pretty simple, it uses Zam's ability to break down Specs Keldeo's checks like Toxapex, Mega Venu, and Mega Lati@s and vice versa, with Keldeo slamming Scarf LandoT, Celesteela, and Heatran. Zam also acts as a nice revenge killer for the team. Things that Zam can struggle to break through, like AV Tang, can be dealt with by Mamoswine, who also provides some strong priority for the team.
Heatran and Ferro provide a nice, strong defensive backbone for the team, and Scarf LandoT provides a nice way to remove hazards and adds some momentum through U-Turn.
HP Ground on Keldeo is just in case Zam dies and you still need a way to deal with Pex, but Focus Blast is a nice 2HKO on Celesteela, but so is Hydro Pump as well. Thanks to
mellowyellowhd for recommending Icy Wind as an alternative to Focus Blast on Keldeo, Icy Wind carries a nice Speed drop that can catch a faster scarfer like Jirachi or something on a switch-in.