Moves
Stealth Rock chips away at the foe's HP every time they switch in and provides fantastic support for teammates. Probopass is a decent user of the move, as it can set it up with ease on almost any trapped Steel-type without worry of the opponent switching to Xatu or a Rapid Spin user or Defogger, but it will struggle in other circumstances due to its passivity. If the team already has a Stealth Rock user, another coverage move can utilized such as Flash Cannon to provide better neutral coverage and hit Fairy-types such as Mega Audino and Clefairy for super effective damage. Volt Switch is another coverage option if the team already has a Stealth Rock user, providing offensive momentum for teammates and hitting Defog users such as Mantine and Pelipper for 4x super effective damage. Toxic can also be used here to cripple Pokemon such as Gastrodon, Claydol, and Hariyama that would otherwise have no problems switching into Probopass. Earth Power hits Pokemon Probopass likes to trap such as Steelix and Aggron for maximum damage while also having the added benefit of hitting Fire-types such as Pyroar and Magmortar and Rock-types like Rhydon, Regirock, and Aurorus. Hidden Power Fire is also a viable coverage move for Probopass, hitting Pokemon such as Ferroseed, Vivillon, and Scyther harder than Earth Power without anything being immune to it. Although this might seem appealing, Hidden Power Fire is usually inferior to Earth Power, as it is far weaker, and Probopass can Taunt Steel-types such as Ferroseed and chip them with Earth Power regardless. Magnet Rise is crucial, as it allows Probopass to effectively trap Steel-types without having to fear 4x super effective Earthquakes. It is also useful for making Probopass harder to revenge kill for the likes of Archeops, Tauros, and Kangaskhan after it has trapped a foe. Similarly, Taunt is valuable because it prevents trapped Steel-types from setting up entry hazards before they faint and can prevent a setup sweeper from boosting any further in a pinch.
Set Details
Maximum Special Attack investment with a Modest nature allows Probopass to hit as hard as possible, while 84 Speed EVs allow Probopass to outpace uninvested base 50 speed Pokemon and below, such as Regirock and tank Rhydon. The rest of the EVs are poured into Probopass's HP stat to allow it to be as bulky as possible. If your team is particularly weak to Piloswine, an alternate EV spread of 252 SpA / 120 Spe / 136 HP can be used to outspeed it and easily win the matchup with Flash Cannon. Magnet Pull is the entire reason one uses Probopass and allows it to fulfill its job of trapping Steel-types. Air Balloon is the item of choice, as it prevents Steel-types such as Steelix from simply using Earthquake against Probopass as it switches in to trap them.
Usage Tips
Aside from Steelix, beware of switching Probopass directly into Steel-types such as Aggron and Ferroseed, as Probopass is KOed by Aggron's Superpower and cannot beat Ferroseed if it is affected by Leech Seed and lacks Hidden Power Fire. Since Probopass is also very one-dimensional, your opponent will often predict you to switch in Probopass on their Steel-type and switch out first, so finding opportune times to trap said Steel-types is essential. In order to trap a Steel-type, it is often useful to sack another Pokemon on your team to said Steel-type and then trap it as the opponent does not have a chance to switch out predicting Probopass to come in. Once Probopass has trapped the opposing Steel-type and set up Stealth Rock, it is often dead weight and potential setup fodder, so beware of just throwing it out recklessly in the midst of battle, as it is very easy to take advantage of.
Team Options
Pokemon that struggle to break through Steel-types such as Scyther, Kangaskhan, and Swellow make for excellent teammates. Other Pokemon such as Archeops, Tauros, and Jynx that appreciate Stealth Rock also work well with Probopass. Furthermore, Pokemon that resist Fighting, Ground, and Water such as Garbodor, Torterra, and Mesprit respectively make for good partners with Probopass, as they have good defensive synergy. Mesprit, in particular, works well with Probopass, as not only do they have fantastic offensive and defensive synergy, but Mesprit can also provide Stealth Rock, freeing up a slot for Flash Cannon on Probopass. Versus teams without a Steel-type, Probopass often finds it difficult to set up Stealth Rock due to its low Speed and multitude of weaknesses, so Mesprit can fulfill that role. Pokemon that make excellent use of U-turn and Volt Switch such as Scyther and Rotom are solid partners for Probopass, as they provide free switches into Steel-types Probopass yearns to trap.