Other move options: Explosion, Flash Cannon, Magnet Rise, Taunt, Thunderbolt, Toxic
Other item options: Air Balloon, Chople Berry, Safety Goggles, Shuca Berry
Notes: Probopass must always outspeed uninvested base 50 in order to outspeed Mawile.
172 HP EVs is divisible by 16, meaning Probopass would take 1 more damage from hazards and status. The 4 EVs is instead dumped into speed.
Groundinium Z allows offensive Probopass to OHKO defensive Probopass, and therefore it needs to outspeed defensive Probopass to avoid Volt Switch.
Flash Cannon hits Silvally-Fairy and Golem
Magnet Rise allows Probopass to fool Golem into switching in and then take advantage, but only should be done if you don't mind rocks going up.
Magnet Rise also allows Probopass to take on Metang more consistently, but it should be noted that Metang does not OHKO either of the above spreads.
Air Balloon allows Probopass to get in on ground moves when it otherwise couldn't, but is highly risky and can cost a lot of bulk from Leftovers.