Alter Aeon Online Help

Keywords are:  'helpful important critical spells skills usefulness exigency'

Most spells and skills are labeled as helpful, important or critical.
This designation is relative to a spell or skill's primary class.

Critical spells and skills are necessary to get the full benefit a
class has to offer. You should learn critical abilities as they become
available when you level. Examples include cleric healing spells such
as soothe wounds and major heal, warrior power attacks such as leap
attack or necromancer animation spells such as clayman.

Critical abilities can be learned without a teacher.

There are no critical spells or skills beyond level 30 for any class. 

This does not mean there no abilities worth learning beyond level 30,
just that your choice of second and third class will have a greater
influence on what skills and spells will work best for you.

Important skills and spells supplement critical class features, but
can be skipped or learned later as you level or gain practices. Examples
would include mage elemental defensive spells or thief ranged attacks.

Helpful skills and spells are beneficial, but not necessary to play
the class. They range from minor buffs, situational attacks, niche
defenses and various utilities.

You can use helpful, important and critical as arguments for slist,
to sort skills and spells into lists by usefulness. They also work
as arguments for the 'check' command.

IMPORTANT - these descriptors assume that the spell or skill's
class is your primary class. Many critical and important abilities
are not as useful if a class is your third or lower. Look up the
help pages for spells and skills, and feel free to ask other players
for suggestions.