Macros and combination attacks
The macro menu is the most important screen in the game, and it sits tucked away where a lot of players never bother to look. You can program up to eight macros (each one a fixed set of actions for the whole party, set up outside of battle), and they're the only practical way to land the game's 14 combination attacks. A combo only fires if the required techniques go off back to back with nobody, ally or enemy, acting in between, so trying to time one by hand almost never works. Build it into a macro and it just happens on command.
Early on, Triblaster (Chaz's Tsu plus a Foi and a Wat from two other casters) throws a three-element beam at everything and carries you through the opening dungeons. Later the combos turn ridiculous: Black Hole, from Rune and Kyra, is flat instant death to every enemy on screen, and Lethal Image, from Alys and Rika, does nearly the same. Against the recurring incarnations of Dark Force, Grand Cross (Chaz's Crosscut into Rune's Efess) is a wave of light tuned to shred exactly that kind of enemy. People call Phantasy Star IV the easy one in the series, and the macro screen is a big part of the reason why.
Demi and Wren play by different rules
The two androids run on a completely separate system, and the game barely explains it. No healing technique touches them: Res, Gires, Nares, even a Trimate, all wasted. Demi and Wren patch themselves with their own Recover skill on the field, regenerate HP just by walking around, and if one drops in battle it revives itself on its own. The only outside fix is a Repair Kit. So the reflex to nurse them with your party healer is exactly backwards; they're the most self-sufficient bodies you've got.
They can't learn or cast techniques and only equip guns, but their skill lists carry their weight. Demi's Barrier shores up everyone's mental defense before a magic-heavy boss, and her Medical Power revives and heals the whole organic party between fights. Wren is a walking artillery piece who picks up hit-all skills like Burst Rockets and, eventually, Positron Bolt. Treat the pair as durable damage and support that you never pour healing into, and your real healer is free to keep the four fragile party members alive.
How do you actually beat Zio?
Zio is where the game quietly checks whether you've been paying attention. The first time you face him at his fort, you can't win. He throws up MAG.BARRIR, which drops magic damage to a flat 1 and makes your normal attacks miss too, and the scene resolves the way it's going to resolve no matter what you try. Don't waste items hammering at it. Just outlast the round count and let it happen.
The real fight comes later at Nurvus, and it opens the same way, with MAG.BARRIR going up first thing. The fix isn't more levels, it's the Psycho-Wand. Hand it to Rune and use it as a battle item rather than swinging it as a weapon, and it cancels the barrier outright. After that the fight is ordinary: stack Deban from Rika, Barrier from Demi and War Cry on Gryz early, then have Chaz lean on Crosscut while Rune deals the heavy magic. Zio answers with Hewn, Corrosion and Black Wave, so keep a healer honest, and he goes down in eight to ten rounds. Walk in around level 19 or 20 and you'll have the room to absorb a mistake.
The Megid trap: say no to get the best technique
Once you've claimed Elsydeon, Anger Tower opens on Rykros, just west of the Courage Tower. Chaz climbs it alone and has to put down a phantom of Alys at the top, only 420 HP and nothing dramatic, before a being called Re-Faze appears as a ball of fire and asks whether Chaz wants to learn the forbidden technique Megid.
Say no. This is the one moment in the game where the obvious greedy answer gets you killed: pick "Yes" and Re-Faze immediately casts Megid on Chaz, an instant unavoidable death with no fight to win and no way around it. Refuse, and Re-Faze decides you've kept hold of yourself and hands Megid over anyway. The head-fake is worth it. Megid slams every enemy with a huge burst of light damage and becomes Chaz's heaviest hit when you reach the final dungeon.
Who should your fifth character be?
Just before the end the game lets you pick a fifth member (Hahn, Gryz, Demi, Raja or Kyra) to round out Chaz, Rika, Rune and Wren. Take Raja. The Profound Darkness is a three-stage marathon, and Raja is the only character who can both keep the party topped off and refill its TP through Ataraxia, which is exactly what a nine-to-twelve-round slugfest bleeds out of you.
The first stage only hits one target at a time, so single-target healing keeps pace. The second stage turns to party-wide attacks like Distortion and Lightshowr, so you'll want group heals going. The third stage is the one that catches people: it casts Canceling, which strips every buff you've stacked: Barrier, Deban, Saner, all of it gone in a single move. The instant it lands, re-apply Deban with Rika and Barrier with Wren before doing anything else, then go back to hammering with Chaz's Megid or Crosscut. Bring Chaz in around level 49 with the rest in the high 40s and you've got a cushion for one bad round. If you'd rather feel that wall out for yourself first, the whole game runs online right here in the browser, so grinding those last few levels never means digging out a cartridge.
Don't let anyone hit level 99
This bug belongs to the original cartridge, which is exactly the version running here in the browser; the later Wii and Mega Drive Mini re-releases quietly patched it out. Push any character all the way to level 99 and the game breaks in a nasty, silent way: every party member's level snaps back down to somewhere around 40 to 50, and each level-up after that drags it lower still, all while the stats screen keeps cheerfully reporting 99. Nothing in the game demands that much grinding, so there's no real reason to climb near the cap. If you like to over-level before bosses, just keep half an eye on your strongest character and you'll never trip it.