Toxic Spikes + Rapid Spin: Actually forgot that Forretress can learn Toxic Spikes and Rapid Spin, so if you want that role, Forretress is your only option other than Smeargle (that isn't weak to electric and is fully evolved). Forretress also has Sturdy, and its only weakness is Fire, which Milotic resists.
Toxic Spikes + Offensive Pressure: Nidoking is immune to electric moves and has a wide variety of coverage that works well in conjunction with Sheer Force. Greninja is a fast option that will get up a Toxic Spikes most of the time, although this encourages Thunderbolt spam. Nihilego is a third option that is slightly slower than Greninja, but way more bulkier. It has a lot of common weaknesses though, so be wary of that.
Hope this helped!
/ds toxic spikes, rapid spin, natdex, all and
/ds toxic spikes, natdex, all in a showdown chat room