dtgreene: Ramialf will reveal hidden monsters.
Also, I believe the chance of staying hidden is affected by speed, which can be manipulated by casting (la)skorech.
You are not meant to fight that boss until much later, and you should bring a level 26+ thief to steal from it. (If level 26+ sounds impossibly high, you are not ready for this boss. Trust me.)
rayres2007: I am wondering how important it is to have a thief steal equipment from floor bosses. I am debating changing my bard into a cleric then a servant or a cleric then a thief.
Thanks.
Rob
For the floor bosses I checked, the equipment doesn't seem to be that crucial, and much of it can be found elsewhere. Not every boss has stealable equipment either.
On the other hand, at the start of the final bonus dungeon, you will encounter a boss that attacks with a Holy Saber for 800+ damage. That boss you will want to steal from. (Fortunately, it is only level 50 and has only 5 Agility.) Note that I once saw that boss appear as a normal enemy.
You can actually keep stealing from an enemy multiple times until you get everything. Just remember to disarm the enemy first. (Note that some monster weapons, such as Strike, are not disarmable. Unfortunately, the game isn't particularly informative about that, so you might want Dice of Fate.)
By the way, the Holy Saber is only usable by third-gender non-Devilish Lords. The other item the boss has equipped is useful for spellcasters, but has its downsides (but is actually not cursed),