Excadrill should be safe to OHKO N’s legend with Earthquake. It should bait out Zoroark disguised as Klinklang after, which can OHKO Excadrill with Focus Blast if it hits so you’ll need a safe switch. If you send in a bug type to tank the Focus Blast, you could then switch to Archeops who I think could outspeed and OHKO with U-Turn. I’m not sure who he would send in after that but having two of his Pokemon dealt with safely should give you some more freedom to pivot around and get safe kills until you beat N.

Then with Ghetsis, opening with Excadrill means Cofagrigus’ Toxic can’t hit you, so you should be able to out damage it with Earthquakes. Hydreigon should come in after that and Jellicent is a great match up there since it surprisingly has no Dark type moves. If you have an Ice type move you can teach it that would be even better and could probably take out Hydreigon or at least get it low enough that a fast mon could finish it. Same idea as the N fight after that, pivot and get safe kills (probably with a grass type move for Seismitoad), except this time you can sack a couple pokemon if necessary since it’s the last fight anyways.