OSRIC Enhanced Combat

I. Core Combat Mechanic: THAC0

This system uses "To Hit Armor Class 0" (THAC0). Your character's THAC0 improves as they gain levels in their class. Refer to class progression tables for base THAC0 values (see Appendix Table 54).

Attack Roll: To hit an opponent, roll 1d20. You hit if the result is equal to or greater than your THAC0 minus the target's Armor Class (AC).

To-Hit Number = Your THAC0 - Target's AC

Modifiers: Your THAC0 can be modified by factors like Strength bonuses (for melee/thrown weapons, and potentially special bows), Dexterity bonuses (for missile attacks), magical weapon bonuses, situational modifiers (like attacking from the rear [+2] or flank [+1], firing at range, cover, etc.), and penalties for using weapons you aren't proficient with.

Natural Rolls: A natural roll of 20 on the d20 usually hits, regardless of modifiers or AC, while a natural roll of 1 usually misses.

II. Combat Round Structure

Round Length: Combat is measured in rounds, each representing about 10-15 seconds of activity.

Five Steps per Round:

1. Monster Action Determination: The DM secretly decides monster actions.
2. Player Action Declaration: Players declare their characters' intended actions for the round.
3. Initiative: Determine the order of actions.
4. Resolution of Actions: Actions are resolved according to the initiative phases. Characters can abort their declared action but act last if they do so.
5. End-of-Round Resolution: Resolve fatigue, retreats, morale checks, and ongoing effects like poison or spell durations.

III. Initiative

Initiative Roll: At the start of each round, both sides roll 1d10. The side with the lowest roll wins initiative for the round.

Action Phases: Actions are resolved in five phases: Very Fast, Fast, Average, Slow, Very Slow.

Resolution Order: Within each phase, the side that won initiative acts first. Actions (attacks, spell completion) happen before movement within that phase. Faster phases always resolve before slower phases, regardless of who won initiative overall.

Determining Your Phase:

• Base Initiative: Determined by size (e.g., Man-sized = Fast), modified by movement rate and encumbrance.
• Weapon Speed: Weapons have speeds (Fast, Average, Slow, Very Slow). (See Appendix: Weapon Speed Table).
• Final Phase: Your action occurs in the later of your Base Initiative phase or your Weapon Speed phase. Magical bonuses can improve weapon speed. Spells have phases based on casting time.

Special Rolls:

• A roll of 1 speeds your action phase by one step.
• A roll of 10 slows your action phase by one step.
• A tie results in a Critical Event (roll on the Critical Event Table). (See Appendix: Critical Event Table).

IV. Movement and Position

Battle Map: Assumes use of a grid (1 inch = 5 feet recommended) for positioning and facing. Facing (Front, Flank, Rear) is important for attacks.

Movement Rate: Your base movement (e.g., Human 12) is adjusted by Strength/Dexterity bonuses and encumbrance. Each point allows moving one 5-foot square. Diagonal movement costs 1.5 points per square (or 3 points for 2 squares).

Movement Categories & Actions: Your chosen action determines how much you can move:

• No-Move: Allows a 1-square adjustment. Actions: Attack, Cast Spell, Cover, Fire (full ROF), Guard, Parry, Use Magical Item.
• Half-Move: Move up to half your rate. Actions: Attack, Charge (partially), Fire (half ROF), Guard, Unarmed Combat, Withdraw.
• Full-Move: Move up to your full rate (or more). Actions: Charge, Move, Run, Sprint.

Movement Timing: Movement starts in your base initiative phase and occurs in half-move increments over consecutive phases if needed. Actions typically resolve after movement is complete, except for Charges.

Threatened Status: Being adjacent to an enemy capable of attacking you makes you "Threatened". Performing certain actions while threatened (like moving away without Withdrawing, turning your back, casting spells, firing missiles) provokes an Attack of Opportunity from the threatening enemy.

Attacks of Opportunity (AoO): An immediate free melee attack granted when an opponent leaves themselves open. You get a limited number per round (Warriors: 3 + 1 per 5 levels/HD; Others: 1 + 1 per 5 levels).

V. Combat Actions

• Attack: Make normal melee attacks. Can be No-Move or Half-Move. Multiple attacks from high level resolve one per phase after the first. May include options like Block, Disarm, Trip, etc. (DM discretion or detailed in supplements).
• Cast a Spell: Starts in Very Fast phase, completes in spell's phase (based on casting time). Interrupted if damaged before completion. Lose Dexterity AC bonus while casting. May allow half-move after if not Very Slow.
• Charge: Full-move action, move 1.5x normal rate. +2 attack bonus, -1 AC penalty, lose Dexterity AC bonus. Attack resolves immediately upon reaching target. Setting spears/pikes is effective against charges.
• Cover: Aim a readied missile weapon (bow/crossbow) at a target/square. Requires proficiency. Get initiative vs target, first shot is Fast/Very Fast. +2 attack bonus on first shot. Can also cover helpless target with melee weapon.
• Fire/Throw Missiles: No-Move (full ROF) or Half-Move (half ROF). Weapons less than 1/round ROF allow half-move only on first shot. Provokes AoO if threatened (except when enemy first closes). Multiple shots resolve one per phase after the first.
• Guard: No-Move or Half-Move. Wait for opponent to enter threatened squares, then attack immediately, potentially preempting their action. Effective against charges (Set for Charge).
• Move: Full-move action. Move up to normal rate.
• Parry: No-Move action. Focus on defense, potentially improving AC or blocking instead of attacking.
• Run: Full-move action. Move up to double normal rate. Cannot attack.
• Sprint: Full-move action. Move up to triple normal rate. Cannot attack, -2 AC penalty, lose Dexterity AC bonus.
• Unarmed Combat: Engage in Brawling, Wrestling, or Martial Arts. Can be No-Move or Half-Move. Provokes AoO if engaging an armed, threatening opponent without appropriate skill.
• Use A Magical Item: No-move or Half-move depending on item activation time (DM discretion, often similar to spell casting time).
• Withdraw: Half-move action. Carefully disengage from one threatened square to an adjacent square without provoking an AoO. Cannot attack.

VI. Damage & Healing

Hit Points: Determined by class Hit Die (e.g., Fighter d10, Cleric d8, Mage d4) + Constitution modifier. HP represent physical endurance, skill, and luck. Reaching 0 HP typically means unconsciousness; reaching -10 HP means death.

Weapon Damage: Determined by weapon type (See Appendix: Weapon Damage Table). Add Strength modifier for melee/thrown. Magic weapons add bonuses.

Critical Hits (Optional): On a successful hit roll meeting certain conditions (e.g., natural 20 beating AC by a significant margin, DM discretion), apply extra effects such as double damage dice or other critical results detailed in supplemental tables.

Healing: Natural healing is slow (typically 1 hp/day rest). Magical healing (cleric spells, potions) is more common.

VII. Other Combat Rules

• Weapon Specialization (Optional): Fighters (and optionally Paladins/Rangers) can specialize for bonuses to hit, damage, and attacks per round. Style Specialization may also be available. (See Appendix: Warrior Attacks Per Round).
• Turning Undead: Use standard Turning Undead rules/table (See Appendix: Turning Undead Table). Clerics turn based on level; Paladins turn as Cleric 2 levels lower.
• Firing Into Melee: A risky proposition. Determine randomly which figure (friend or foe) in the melee is struck if the attack roll indicates a hit but misses the intended target's AC. A system assigning points based on figure size can refine random determination.
• Cover/Concealment: Provides AC bonuses and improves saving throws vs. area effects. (See Appendix: Cover and Concealment Modifiers).
• Non-Lethal Combat: Rules for subdual attacks, punching, and wrestling allow characters to subdue opponents without killing them.

Appendix: Referenced Tables