Core Mechanics

Gem's core system is based on D20 table-top RPG systems. 


Gem’s combat system is based on D20 table top RPG mechanics. We’ve made some changes that we hope will provide a balanced game - given the range of player levels and additional variable ship mods added to the system.

Targeting vs. Evasion

Space is big. So in order to attack another ship, you have to first target and intercept them. A D100 roll establishes the chance the attacking ship has to intercept its target. 

Each ship has a base targeting rate of 75%. 

If the D100 roll is between 1-75, the attacking ship has successfully intercepted its target. The attacking ship can increase the odds of successfully intercepting a target by installing targeting mods. The defending ship, can offset the targeting mods by installing evasion mods. 

Example: Ship A attempts to intercept Ship B. Ship A has a +25% targeting mod installed. With the base targeting rate of 75%, Ship A has a 100% chance to target Ship B (Provided Ship A doesn’t roll a 1 and critically fail!). 

Ship B, however, has evasion mods installed totaling +60% evasion. Ship B’s evasion total is subtracted from Ship A’s total targeting chance, bringing the 100% down to 40%.

If Ship A’s D100 roll ends up being a 60, Ship B would evade the attack and combat would not initiate since Ship B’s evasion mods had reduced Ship A’s range of success from 1-75 to 1-40.

Attack vs. Defense

Upon a successful interception, combat is initiated. The attacking ship’s attack roll is as follows:

Attack = D20 + 25% Pilot’s Level (rounded down) + Installed Attack Mods + Ship’s Base Attack Bonus.

The attack is compared against the target ship’s defense roll:

Defense = D20 + 25% Pilot Level + Installed Defense Mods +  Ship’s Base Defense Bonus 

Defense = D20 + 50% Ship Level*
*50% of the NPC ship level is used instead of 25% to account for the attacking ship’s mods.

After an attack is made, the defending ship returns fire, using the attack/defense mods respectively. 


Upon a successful hit, damage is done to the target.

Damage = 4D10 + Installed Damage Mods

NPC (Damage done against player)
Level 1-20 = 4D10
Level 21-40 = 6D10
Level 41-60 = 8D10
Level +100 = 10D10

Note: Damage done is doubled if player rolls a natural 20.

If player has damage reduction and/or damage reflection mods installed, those come into effect here. 

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