Phantasy Star II. I want to say it's my favorite out of the Original Series, and it's true, but... let's face facts, everyone. It's about as sluggish and slow as Phantasy Star III, the combat is less JRPG combat that we're used to and more "Keep doing this, press button to intervene and change tactics," Techniques are less "hit this enemy with elemental damage to hurt him more" like in Phantasy Star IV and more "hit slightly harder," and the confusing first-person mazes from Phantasy Star I are replaced with confusing third-person mazes. (That last one's not even my own; I got it from The Cutting Room Floor.)
It's still got its charm. But... holy crap, I've never seen an RPG with stats as... I hesitate to call them user-unfriendly; Final Fantasy I for the NES was user un-friendly. PSII is user-mendacious. Almost nothing works as expected.
Let's start with the least-broken and work our way down the list.
Hit Points (HP) and Technique Points (TP) work as intended. Hit Points measure how much physical abuse a character can take, and once they hit the big goose-egg, that character's body bag filler. Technique Points represent how much psychic power a character's capable of using before they're exhausted and have to whip out the hunting rifles.
Agility determines the party's initiative order in combat; generally, the higher it is, the faster a character acts in a round. There may be a little bit of fudging behind the scenes to randomize the order, though. This is improved by equipping footwear. Anna's Ner Technique and Amy's Saner Technique boost Agility by +10 for an entire combat, and repeated manifests stack. (Saner is more cost-effective due to Amy having more Tech Points overall, and four uses of Ner are more expensive than one use of Saner.)
Defense reduces incoming damage. Not surprisingly, armor helps improve this. Amy's Shu and Sashu Techniques boost Defense by 20 for the duration of one combat to one target (Shu) or the whole party (Sashu). Sashu is more cost-effective, and I think it stacks with itself.
Dexterity works more or less as intended, too. Roughly, each character has a 90% accuracy with their attacks; having a higher Dexterity than a target's Agility increases that to 100%; having a lower Dexterity reduces that to 80%.
Luck does what the manual says it does and helps determine the accuracy of enemy special attacks. It's not a 1:1 thing, though. It's in blocks. Less than 50 Luck? Nothing happens. 50 to 99 luck grants a -10% accuracy bonus to enemy specials; 100 to 149 grants a -20% accuracy, and 150+ Luck grants a -30% penalty.
Now, the fun one. Attack helps determine a character's damage bonus to attacks. Each weapon has a specific amount of damage that it does, and a character's Attack stat increases that roughly 1% for each point of Attack. It looks like a character's Attack stat improves when you equip better weapons, right? PHANTASY STAR II LIES. The boost is cosmetic. The only things that help improve your Attack stat are leveling up, Knife Boots, and Anna's Shift Technique (which gives her +20 Attack per use.)
Oh, and I should mention that guns in PSII work like guns in PSI. They do a fixed range of damage. Attack stat means nothing to them.
Fun fact through research: Amy's second-best weapon, the Silent Shot, is a pistol according to her attack animation with it in PSGen2. Yeah. That's right. That sweet, cute, innocent doctor can pack heat when she needs it.
Rolf: ...Someone tell Rudo to wipe the drool off his chin. Geez. >=/
Strength and Mental... do absolutely nothing. That's right. These numbers are like Charisma in Dungeons & Dragons. They look cool, but serve absolutely no purpose.
That out of the way, I also found out what some of the Techniques actually do. Yeah, they're kinda obfuscated and whoever did the work on the wiki I'm using probably spent a lot of time on this. But essentially:
Brose: Kain points at a robot, they have a 50/50 chance of biting it on the spot.
Conte: Kain picks a robot, it has its special attack accuracy halved. No save.
Vol/Savol: Hugh has a 60% chance of outright slaying one biological target (Vol) or a 70% chance of slaying a group of biologics (Savol.)
Rimit: 50/50 chance of paralyzing one biomonster. Like Amy's Silent Shot but worse. At least that works on robots. I think.
Shinb: Does jack. The Technique's bugged.
Fun stuff, huh? =P