Understanding spells for monsters

[wingsofclarity]

Help me understand how spell-like abilities work for monsters. The ogre mage's description states:


Spell-Like Abilities: At will—darkness, invisibility; 1/day— charm person (DC 14), cone of cold (DC 18), gaseous form, polymorph, sleep (DC 14). Caster level 9th. The save DCs are Charisma-based.

Does "1/day" the ogre mage can cast only one of all those spells or one spell each? Does at will mean as many times at it wants? (so the only restriction would be the action it takes to cast it basically). I just find it awkward that they "... rely on their spell-like abilities, resorting to physical combat only when necessary." and then they can only cast one damaging spell...once..

Thank you.

[Draconium]

Each SLA listed under 1/day can be used once per day, as said.

[Dusk Eclipse]

Obligatory link to Urpriest's Monstrous Monster Handbook (http://www.giantitp.com/forums/showthread.php?207928-Urpriest-s-Monstrous-Monster-Handbook)

[Urpriest]

I don't know if my handbook covers this, but yes, each ability can independently be used once per day, while at-will abilities can be used as many times per day as the creature wants.

They've got a few different disabling spells they can use 1/day, but yeah, that does feel kind of weak. It could also mean they use their at-will invisibility and flight to avoid combat entirely. More likely, the ogre mage is just kind of poorly designed. There were a few fun variants in later books that make for more interesting encounters, including the various Oni in Oriental Adventures and a trio of reasonably cool Elemental Mages in MMV.