Renewable Spell

Some spells can have their duration extended. For example, many Buffs and Debuffs with a set duration can be renewed by the caster when they expire. This requires general Mana be spent at that time. Spells that lie dormant indefinitely until a trigger condition is met, such as the many kinds of warning spell, can be reset with the expenditure of mana from any person present. Renewing a spell is more costly in mana than the original spell; this offsets the convenience of not needing to explicitly cast the spell again.