UltraMicrolite20 Hack

Before I even heard of the OSR I discovered a little gem called Microlite20, by Robin Stacey.  M20 is basically a boiled down version of 3E D&D, slimmed down to around 2 or 3 pages (not including spells and magic items).  But if M20 was still too complicated for you, there was an even slimmer version called UltraMicrolite20…lighter even than the one-page RPG Searchers of the Unknown, if you can believe that.

I’ve been fascinated by UM20 since I first laid eyes on it.  It pares down the D&D experience to its barest essentials and yet retains a high degree of flexibility using M20’s stat + skill mix-and-match system to resolve actions.  At the same time, it is wide open to all kinds of tinkering, tweaking and houseruling.

So, here’s my UM20 hack, which I have cleverly named eXpanded UltraMicrolite20, or XUM20 for short (because X is cooler than E):


Three stats:  Strength (STR), Dexterity (DEX) and Mind

Divide 5 points between the three stats; maximum starting score is 4.

You may reduce one stat to -1 to add +1 to another stat.


Six skills:

Combat – Making melee and ranged attacks

Communication – Social interaction

Knowledge – Lore and book learning

Physical – Climbing, swimming, etc.

Subterfuge – Sneaking, guile and trickery

Survival – Tracking, hunting, land navigation, etc.

Select one skill to be your ‘Tag’ skill.  Your Tag skill starts at +4.  All other skills start at +1.


New characters are assumed to start with basic adventuring gear, plus a primary melee weapon, back-up melee weapon (such as a dagger) and a ranged weapon.  If desired, either the back-up weapon or the ranged weapon can be exchanged for a shield.

Finally, select either light or heavy armor for your character:

No armor = +0 AC; full DEX for AC; move 6 (fast)

Light armor = +3 AC; ½ DEX (round down) for AC; move 5 (moderate)

Heavy armor = +6 AC; no DEX for AC; move 4 (slow)

Shield = +1 AC; off-hand


Roll d20 + relevant stat + skill ≥ DC (set by GM) for success.  Not all actions require a check for success; the GM should only call for a check when the consequences of failure are significant, when time is a consideration or when it’s important to determine the degree of success.


Roll d20 + DEX to determine initiative.

For melee attacks, roll d20 + STR + Combat ≥ target AC to hit

For ranged attacks, roll d20 + DEX + Combat ≥ target AC to hit

Monsters and NPCs use d20 + Hit Dice

AC = 10 + Armor bonus + DEX (modified by Armor worn)

Any PC taking 3 hits in the same battle is unconscious for the rest of the fight; immediately make a DC 15 Phys + STR check to survive.  Most monsters take only 1 hit to kill, though particularly large or tough monsters can take hits equal to their Hit Dice to kill (at the GM’s discretion).

An attack roll that exceeds the target’s AC by 10 or more points is a grievous injury, inflicting 2 hits on the target.

At the beginning of their turn, a character may make two attacks (melee or ranged) against the same target, or against different targets within range.  Both attacks incur a -5 penalty to their attack rolls.

Character Advancement

Each time a character survives a battle they gain 1 XP.  If the GM determines that a battle was particularly long or tough 2 XP may be awarded.  Likewise, the GM may group multiple easy battles together and count them as only a single battle for awarding XP.  At the GM’s discretion, additional XP may be awarded for accomplishing objectives or performing heroic deeds.

You may spend 10 XP to increase all of your skills by +1 each, or you may spend 20 XP to increase one of your stats by +1.  You may also spend 30 XP to take an additional hit in the same battle before going unconscious.

The argument can be made that UM20 is rules-lite to a fault.  Witness the lack of a magic system or different character races (the lack of character classes, on the other hand, is actually a feature of the system in my opinion).  I hope to address some of these shortcomings in future posts in a manner consistent with the rules-lite spirit of M20 and UM20.



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2 Responses to “UltraMicrolite20 Hack”

  1. Ravencroft Says:

    Thanks for this amazing hack for Ultramicrolite.

    You say:
    Most monsters take only 1 hit to kill, though particularly large or tough monsters can take hits equal to their Hit Dice to kill (at the GM’s discretion).

    And that’s fine. But how is the Hit Dice calculated for the monsters? Ultramicrolite say nothing abour that. And Microlite20 only says that monsters have a Hit Dice of d8 and d12. How would this translate into ultramicrolite?

    • EdOWar Says:

      Microlite20 listed a number of monsters by both number and type of hit dice. For example, orcs were usually HD 1d8, ogres might be HD 4d12, and so on. XUM20 just uses the number of Hit Dice, ignoring the type of hit dice. So an orc is 1 HD, an ogre is 4 HD, a troll is 6 HD, and so on. There are plenty of online resources that show the HD for various D&D monsters. Cheers!

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