Arthur in the Ghouls 'n Ghosts games is really fragile. One hit and he loses all his armor, and another reduces him to a skeleton. Which is rather unfortunate since the world he lives in is swarming with monsters, each more lethal than the last.

But, if you're lucky enough, you can get a suit of Gold Armor

which is equally as fragile, but lets you do magical attacks.

What's not immediately obvious is that when you're doing these magical attacks, you have a (very) brief window where you're all but invincible. It's basically as long as Arthur is holding his arm in the air. It's kind of hard to see here, but there's an enemy passing right through him unharmed.

It's really hard to get the timing right, since the window you have kind of depends on the weapon that you have equipped. But if you expect to get any kind of good at this game, then you're going to have lots of opportunities to practice it as you pump the quarters into the machine.

Also, this works in the Super NES port.