OMG, can't believe I forgot about that one. Decades ago, good times indeed.
It's got to be one of the best core game mechanics ever designed. Just simply brilliant. Detailed enough to handle every situation. No charts required (popular back then). But easy enough to quickly memorize.
Remember? It's a percentage based system. Those are always easy. So, you had modifiers like this: Add Stat + Skill, then subtract 30 for (insert reason), and roll that or lower on % dice.
The brilliant part was adding in the three basic difficulty categories. Normally, you use your full total. Some situations, you use half your total. Rare, but extremely hard, situations, you use one quarter your total.
So, if you're damn good with a Walther PPK, and your Stat + Skill = 90, you'd roll 90 or less on % dice most of the time when shooting your weapon.
But, let's say your target is moving. That's a -30 penalty. So, you shoot at the moving target rolling 60 or less on % dice.
Your moving target, though, stops in a parking lot, and shoot back at you. He's covered at the waist down from the car, giving him half cover. When you return fire, your difficulty categories kick in. Half cover means you halve your chance to hit. So, to hit him, you now need a 45 or less on % dice.
You miss, and your target begins running again. That car is still between you, so you've got the difficulty category and the modifier to deal with. It's a tough shot. Bullets are pumping into cars. Alarms are going off. You shot is 15 or less on % dice.
You move up to the car to get a clear shot at your target. But, he reaches the elevator bank and uses the cement wall for full cover, exposing himself only when he whips and eyeball and his right arm around to fire back at you. This means you slip down to the Very Hard category, so your chance of 90 is quartered to 23, when you fire back, trying to hit that eyeball or exposed arm. Maybe tag his shoulder.
What a great, easy-to-use system. Portable to other games. It's too bad that system only saw use in TS/SI. It's one of my favorite mechanics I've ever seen or played with.