As far as the Machamp matchup ToxiTank is definitely the way to go. You can OHKO them w/ Lucario GL out, which you should already be running, and you should already be running Skuntank G with stadiums. And if you get the chance, you can always belt it and/or play down Snowpoint Temple. When it's badly damaged, Poke'Turn, send up Crobat G (or anything else with free retreat), bench Toxicroak G, energy back on, Energy Gain, retreat. You've got a fully restored Toxicroak back out OHKO'ing Machamps. Meanwhile you can charge a Garchomp C for prizes later and when you're down to the last Cyrus (or before then) you can search out an Aaron's Collection to get back Toxi IF they somehow manage to get it KO'd. You've got 4 Poke'Turns, an Aaron's, and that many turns to charge a Garchomp C Lv.X for snipes. I don't think they can kill your Toxi that many times in a row, but just in case.
With Mirror Match, it comes down to who gets the better hand unless you tech for it.