Mythras Core Rulebook has a resource on page 111 for Games Masters - Rabble, and Underlings. These are a great tool to fill a crowd scene with a "cast of thousands." 

What Are Rabble And Underlings?

Neither Rabble nor Underlings need much character generation. The Mythras Core Rulebook has the following to say about Rabble:-

Rabble are foes who intimidate by their numbers but in actual fact have little prowess or willingness to remain in combat once blood is shed. They can take many forms from vicious beggars who set upon drunken characters when they stumble home from the tavern along dark alleyways; or the mindless adherents of a dark cult – eager yet incompetent.

And this is what the Core Rulebook has to say about Underlings.

Underlings are competent foes usually sent en-masse to harass Adventurers: thuggish bodyguards irregular troops in the opening stages of a battle, for example. Despite not being tracked as full characters, underlings can prove deadly if they catch their targets unprepared.

Both are useful tools to pack a combat scene and to give the Adventurers something to hit. However, they are useful to Games Masters in plenty of other ways.

Quick and Dirty Allies and Contacts

An Ally (page 22, Mythras) is:-

a friend, colleague or relation who shares the same cause as the character and will offer help and guidance when called upon. Depending on their personality the Ally may want a favour in return or might provide aid for free.

Contacts (also page 22) are:-
people of potential influence the character knows. A Contact is an acquaintance who can help, not one who will.

There is nothing that says that the Games Master has to generate a full character profile for each and every Ally and Contact. They only need to flesh out enough to provide the service the Ally or Contact can offer to the frtiendly Adventurer - a Skill which the Adventurer does not have (such as Bureaucracy or a specific Lore), a resource such as a mob or a faction artefact, inside information about a faction, or assistance (such as opening the back door of a workplace of a guild which the Adventurers wish to infiltrate).

Contacts need more persuading, and more upfront incentives, than Allies. A Contact may not necessarily believe in the Adventurers' cause, or be motivated to assist. They can, however, possibly be bought, bribed, influenced with incentives, plied with strong drink or expensive food, or taken out on dates if necessary to get them to help.

Whatever the means of influence, however significant the efforts to get them to offer aid, Contacts can be treated the same as Allies - give them just enough stats to get the job done that your Adventurers hire them for.

Instant Ship's Crew

Suppose your Adventurers need to board a pirate ship filled with armed, dangerous, lowlife scum. Here you are. Have at them. Stat up their Move, Action Points, Hit Points, Initiative, and a Combat Style with a percentage. See below.

Instant Backup / Rowdies

Rabble and Underlings can be hazardous to Adventurers, except in one circumstamce - when they are on your side.

There is a great delight in being able to call a mob to your aid, and have them suddenly appear as a great wall of people over the crest of a hill behind you.

Acolytes and Congregants

A ready source of Magic Points for Tap spells, Enslave, or to draw upon donated Devotional Magic Points (Mythras, page 180). Theists, in particular, can call upon a suitably large congregation for their Devotional Magic Points to power a Theist Miracle such as Behold, Propitiation, Consecrate and so on. Only a few Magic Points are needed, and each congregant need only donate one Devotional Magic Point; the rest probably go to feed the deity.

Service Personnel

This is probably where Rabble and Underlings come into their own - whenever the Adventurers need to speak with a bureaucrat, buy something from a shop, or generally pay for someone's services on a regular basis to the extent that they get to know the service provider's name, generate these minor recurring support characters as Rabble or Underlings.

Household Staff

For Adventurers who lack the subtle skills needed to run a household, anything from Mechanics and Engineering to Bureaucracy and Commerce, household staff are just the thing. Give each staff member a name, a smattering of personal details, and a decent level in a relevant skill or two (such as Craft (Cooking), Bureaucracy, Commerce and so on), and that is generally all you need.

Troupe of Entertainers

Whether you need a noisy, gaudy distraction out front while your gang sneaks in the back, or you need to infiltrate a stronghold under the guise of a wandering troupe of entertainers, nobody can pack the crowds in quite like a well-trained troupe of singers, street acrobats, street magicians, mummers or a band, with or without singers.

Creating Rabble and Underlings

Rabble and Underlings are average in every regard, unless you ve got a recurring Underling whom you might want to upgrade to a full-on recurring non-player character later on in the campaign.

Used for combat, Rabble and Underlings have average Initiative and Magic Points, as well as a standard Move of 6 and the usual 3 Action Points. Rabble tend not to wear armour. Underlings can wear armour, and it's typically 1 or 2 AP if they are wearing armour at all. Their Hit Points are also about average, based on CON 11 and SIZ 13. As a rule of thumb, give Rabble 5 Hit Points and underlings 6.

The last thing you need is to give them at least one relevant skill. For violent thugs sent to harass the Adventurers in a back alley encounter, give them a relevant Combat Style such as Thug. As for the skill rating, it is either 30% for incompetent rabble, 60% for competent rabble, 60% for incompetent underlings, and 90% for competent underlings. Rabble cannot use Special Effects. Underlings can. For the sake of completion, they have Evade, Endurance, Unarmed, and Willpower at the same percentage as their Combat Style.

Care and Maintenance

Both Rabble and Underlings aren't cheap. The "Goods and Services" section of Fioracitta, The Heart of Power provides a table for service costs and service providers. Use those costs as a basis for how much money you think the Adventurers should part with. Charge the going rate in SP for a relevant skill of 60%; halve the price for a relevant skill of 30%, and inflate the base cost by 1.5 for Masters with a relevant skill of 90%. Round up, every time.

Promotion

As Games Master, you can gradually move the Rabble or Underling non-player character closer to becoming a full-blown Non-Player Character or even replacement Adventurer over the course of the campaign. Keep careful track of all their relevant skills, and add no more than one new element (such as a skill) between adventures. For instance, a Loremaster might have a lot of Lores at 60%, and even more Lores at 30%, but you can add Teach at 90% at one point, and introduce this in a scene where the Adventurers stumble across their Loremaster teaching a very large class, or Swim if the Adventurers stumble across the Loremaster going for a dip in Lake Lascha, far from her usual stacks of dusty tomes.

Journaling

Making the Rabble and Underling characters recurring, particularly Allies and Contacts, gives you a chance to turn your Adventurers from cardboard heroes into full-fledged personalities, with likes and dislikes, and give them people in their lives and down times they can relate to between adventures.

They can also provide a useful tool to allow you, as Games Master, to inject a little common sense into a situation. If the Adventurers are going to attempt something stupid, their tagalong rabble member can tell them when there's an alternative available (with an easier grade of skill and less chance of dying of a fumble).

Journaling is the most efficient tool for keeping track of your Rabble and Underlings. Note down all the details for each person, and bring your journal with you to each game. Leave space on each page to add details as they crop up such as revealed skills, relatives, and so on. You need never forget an important secondary character's name again.

Minor Players, Major Uses

By using Rabble and Underlings, the Games Master can supply a host of throwaway characters for the Adventurers to interact with. You can produce them in a hurry without needing to spend an hour in character generation per person. These background characters can be presented as people, with their wants and needs, and they can be just as significant to the Adventurers as the full-fledged enemies they have to face in the course of their adventures.