Solos are a part of Warmachine and Hordes that are capable of augmenting your army in a plethora of ways. Each faction has access to at least a half a dozen in-faction solos as well as Mercenary and Minion solos which they can hire.
Each faction will use their solos in a different fashion and often times it depends entirely upon the list you are making. Most list I have seen have about two or three solos but there are lists with up to six or seven used at once. Lets take a quick look at the most common solos you will see regardless of faction for Warmachine.
Gorman di Wulfe:
The mad bomber. The crazy alchemist. Call him what you will but this guy is one of the most common solos in the game because of his utility and he works for all Warmachine factions. His specialty is throwing one of his three bombs at the enemy. One is an acid grenade and is capable of melting most infantry in the AOE. His second is his Rust bomb and if it lands on a Warjack then the 'Jack suffer -2 to its ARM stat making those tough Khador 'Jacks much more reasonable to deal with for everyone. His last and most amazing bomb is his Black Oil grenade. Any model hit will suffer -4 to its MAT and DEF. It also stops running, charging and spell casting. If this hits a Warcaster like Caine or Morguoul - then you have probably won the game. Very few casters can survive with such a massive DEF loss and it is normally game over at that point.
The mad bomber. The crazy alchemist. Call him what you will but this guy is one of the most common solos in the game because of his utility and he works for all Warmachine factions. His specialty is throwing one of his three bombs at the enemy. One is an acid grenade and is capable of melting most infantry in the AOE. His second is his Rust bomb and if it lands on a Warjack then the 'Jack suffer -2 to its ARM stat making those tough Khador 'Jacks much more reasonable to deal with for everyone. His last and most amazing bomb is his Black Oil grenade. Any model hit will suffer -4 to its MAT and DEF. It also stops running, charging and spell casting. If this hits a Warcaster like Caine or Morguoul - then you have probably won the game. Very few casters can survive with such a massive DEF loss and it is normally game over at that point.
Rhupert Carvolo, Piper of Ord:
The Pied Piper if there ever was one. While he only works for Protectorate of Menoth and Cygnar, he is also very common because of the utility and buffs he brings to your infantry. The Piper pipes, as I'm sure you figured out, and he has three different tunes he can preform each turn. Heroic Call gives that unit Tough and Fearless making them more survivable and is excellent when you see guns on the other end of the table. Just remember Tough is random so don't expect too much but if you have an anti-knockdown option as well it can be quite powerful. Dirge of Mists grants a minor bonus to DEF and gives the unit in question Terror so you can charge into the enemy and force a command checks . Finally you have March which gives the unit Pathfinder. This is especially important since you can't charge over walls without Pathfinder.
The Pied Piper if there ever was one. While he only works for Protectorate of Menoth and Cygnar, he is also very common because of the utility and buffs he brings to your infantry. The Piper pipes, as I'm sure you figured out, and he has three different tunes he can preform each turn. Heroic Call gives that unit Tough and Fearless making them more survivable and is excellent when you see guns on the other end of the table. Just remember Tough is random so don't expect too much but if you have an anti-knockdown option as well it can be quite powerful. Dirge of Mists grants a minor bonus to DEF and gives the unit in question Terror so you can charge into the enemy and force a command checks . Finally you have March which gives the unit Pathfinder. This is especially important since you can't charge over walls without Pathfinder.
Epic Eiryss, Angel of Retribution:
The dirty elven hooker. There I said it and I'm sure you will say it soon. Eiryss is special for two reasons. The first is that she is the only Solo in the game who has an Epic and Prime form like Warcaster and Warlocks. The second and more important reason is because she is capable of stripping upkeeps, animi and Focus on any model, including Warcasters. She is brought in many lists for her utility, especially in factions like Khador who can't stop enemy upkeeps without her. She also is capable of disrupting Warjacks so they can't be given Focus which is powerful in stopping charges or other abilities. I could honestly write an entire article on this model alone but I hope that this blurb gets the point across. She works for Cygnar, Protectorate and Khador and is considered to be a Retribution model when used in their lists (damn elves working together).
The dirty elven hooker. There I said it and I'm sure you will say it soon. Eiryss is special for two reasons. The first is that she is the only Solo in the game who has an Epic and Prime form like Warcaster and Warlocks. The second and more important reason is because she is capable of stripping upkeeps, animi and Focus on any model, including Warcasters. She is brought in many lists for her utility, especially in factions like Khador who can't stop enemy upkeeps without her. She also is capable of disrupting Warjacks so they can't be given Focus which is powerful in stopping charges or other abilities. I could honestly write an entire article on this model alone but I hope that this blurb gets the point across. She works for Cygnar, Protectorate and Khador and is considered to be a Retribution model when used in their lists (damn elves working together).
Reinholdt, Gobber Speculator:
Now I couldn't write an article about solos that your gonna see without none other than Reinholdt, Gobber Speculator (The Bloody Famous). This little bugger only works for Cygnar and Khador and you will normally see him in Cygnar. He is pretty much a mini Warcaster attachment as all of his benefits only go to your Warcaster. His first and most common ability is Reload. He has to be B2B to preform this but the Warcaster can move away once he does this. The next time the Warcaster activates s/he can make another shot with their gun for free. You don't have to pay for it and it increases the use you are going to get with casters like Sloan and eCaine. He also has the Spyglass ability which lets you measure the distance between two models in your Caster's LOS and Lucky Charm which give you an addition dice to attack or damage and you then drop the lowest. This effectively increases your average dice by 2.3 or so. He is more likely to be seen in Cygnar since Cygnar likes him for reload and Khador will normally bring their War Dog for the same point value.
Now I couldn't write an article about solos that your gonna see without none other than Reinholdt, Gobber Speculator (The Bloody Famous). This little bugger only works for Cygnar and Khador and you will normally see him in Cygnar. He is pretty much a mini Warcaster attachment as all of his benefits only go to your Warcaster. His first and most common ability is Reload. He has to be B2B to preform this but the Warcaster can move away once he does this. The next time the Warcaster activates s/he can make another shot with their gun for free. You don't have to pay for it and it increases the use you are going to get with casters like Sloan and eCaine. He also has the Spyglass ability which lets you measure the distance between two models in your Caster's LOS and Lucky Charm which give you an addition dice to attack or damage and you then drop the lowest. This effectively increases your average dice by 2.3 or so. He is more likely to be seen in Cygnar since Cygnar likes him for reload and Khador will normally bring their War Dog for the same point value.
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Now all of the solos I've mentioned are Mercenary solos that you will commonly see on the field. Each faction then has their own incredible solos to choose from and many people won't bring Mercs because they don't see them as necessary. Many will argue that this is handicapping yourself but I rarely run Mercs in my Khador and I don't suffer for it, or at least I rarely do.
There will be more soon!