Controls and the lag you can't fix
Three buttons do the work. Space jumps, L swings the sword, K punches. Hold K for about three seconds and Hercules charges a stronger punch that breaks the rocks blocking the path. The ground stomp (+Space) looks impressive and does nothing. Enemies walk through it. It's a visual effect with no gameplay attached.
The sword only works standing. Crouching disables it, so don't try to duck and swing a low enemy. You can't.
Then there's the lag. Every input lands a beat late, because the engine runs at a low frame rate and there is no fixing it. Forward jumps suffer the most. Tap Space quickly while running and Hercules clears the gap. Hold it a fraction too long and he stops dead, then jumps straight up. Plan one move ahead. If an enemy is already in your face and you haven't pressed anything, you're taking the hit.
What items actually do (and don't)
Only one pickup matters: Herculade. It refills two hearts, sometimes just one. Bottles are rare, so don't burn hearts assuming another will turn up soon. They usually sit after a long enemy stretch, a kind of unspoken apology from the game.
The Achilles helmet grants temporary invincibility. Useful in theory. In practice, the timer is so short it often runs out before you reach whatever you were trying to bypass. Don't plan a run around it.
Everything else is decoration. Coins, Herc dolls, the H-E-R-C-U-L-E-S letters scattered around the levels chime when you grab them and do nothing. No score counter, no bonus life, no completion reward. If a letter sits over a pit of rats or under a stack of falling dummies, walk away. The game will never thank you for collecting it.
How enemies actually work
The sword only hits one enemy per swing. If three rats and a bat all sit inside the arc, the first to register cancels the rest, and the others walk through you untouched. This is why a swarm is dangerous even when you have plenty of room to swing. The math just isn't on your side.
Every enemy gets a moment of invincibility after a hit. Mash L and most swings count for nothing. Connect, wait a beat, connect again. Most enemies fold in two or three hits if you respect the rhythm.
Rats are their own problem. The sword doesn't reach the ground, so you cannot kill a rat that's running on the floor. You have to wait for it to jump, and rats jump on their own schedule. Stand near one and swing pre-emptively as it leaves the ground.
The hit detection is generous on the enemy side, too. A bat or harpy takes a heart off you a couple of pixels before it visually touches Hercules. And the screen doesn't scroll down, so every drop is blind. There are no pits to fall into, but there are enemies waiting at the bottom you can't see until you land on them.
Level 1: the spinning poles and the falling dummies
Hero's Gauntlet looks like a tutorial, then ambushes you twice. Both ambushes have killed more first runs than every boss in the game combined.
The first is the falling training dummies. There's a stretch where wooden dummies drop from off-screen without warning. The drop points are fixed, so the section becomes trivial once you know them. The first time through, you take a hit, sometimes two, and you don't even understand what just hit you. Walk slowly. When you see one land, memorize the spot.
The second is the spinning poles. Seven or so rotating poles strung over a gap, and Hercules has to jump from one to the next to reach a ledge. The collision is barely a pixel forgiving in each direction. Time the jump for when the pole is at its widest visible point, and never try to clear two at once. The rats placed directly beneath the poles are a trap. If you fall, you land on them with no health left to spend.
Smaller note for the same level: the sharks in the water pits die in one sword swing if you hit them before crossing. You can also jump over them. Killing them is safer.
Boss strategies, in order
Every boss in Hercules 2 works the same way: find the one spot where your sword reaches them but their attack doesn't, then swing for five to ten minutes. A full fight runs forty to fifty connected hits. There's no pattern to read and no shortcut.
Level 1 centaur
Stay just outside his arm. Sword hits him, his swing misses you. When he throws a fireball, duck. He only throws one at a time and won't throw the next until the first leaves the screen, so there's no scramble.
Nessus (level 2)
The only boss that can softlock the level. Nessus runs faster than Hercules and won't be stunned by hits. If he leaves the right edge of the screen, he can vanish, and walking back to the far left to respawn him sometimes doesn't work at all. Move slowly toward the platform on the right so he stays onscreen the whole way. Once you're positioned, he runs the same loop over you forever. Sword him on every pass.
Minotaur (level 3)
Throws stone blocks in directions that don't relate to where you're standing. He doesn't react to you, so close the distance and keep swinging. The catch is a block landing on your head at point-blank range. He takes noticeably more hits than the centaur or Nessus.
Hades
Find the platform that puts Hades inside your sword arc when he hovers near you. Stand there. When fireballs come, jump over them. They can still hit you while you're on the platform, so this part is timing, not safety. There's no opening pattern: he comes close when he comes close, and you swing every time he does.
Titan Flight: don't shoot anything
The Pegasus level swaps platforming for a side-scroller and gives you a shooter with no reason to shoot. Enemies drop nothing. There is no score. Killing a chimera, a flying sword, or one of the fairies on flying beetles changes precisely zero variables in your run.
So don't. Find a clear lane above or below each swarm and hold it until they pass. This is the one level you can finish without losing a single life. The trick is to stop engaging.
At the end you free Zeus from a pile of rocks, and a separate title card hands you over to the Vortex of Souls for the Hades fight. The game itself has no checkpoints, no continues, and no passwords; on the original cart, dying sends you back to the start of the current section with no recovery. Playing online in a browser gives you the one safety net the cartridge never had. Save the state before you walk into the Hades fight.