Building Realm Spells is often an art form, but if you are using the Fantasy Fuzion system for Birthright, there are a few guidelines you can use to aid in their construction.  First, construct the desired effect as a Power, as you would normally when beginning the spell construction process.  In addition, the following modifiers can be applied to the spell:

• Province area of affect +15 (Usually required.)
• Increased Casting Time -18 (Required)
• Variable Regency Point Costs:  -2 (Required)
• Variable Gold Bar Costs (2000 gold pieces/bar):  -2  (Usually required.  There may be the occasional elven spell which does not require this.)

Typical total for Realm Spell modifiers:  -7 Power Points.
This means that  usually, a spell caster can cast immensely powerful spells at a relatively low MAGE level.  Assigning Regency Point and Gold Bar costs can be a little less than obvious, but the following provides some guidelines:

• The Spell can kill a bunch of people: 10 RP/War Card Unit or 10 RP/100 individuals.
• Musters troops or Summons monsters: 5 RP/100 or 5 RP/War Card unit, whichever is greater in cost.
• Minimum of 1 Regency Point per province affected or 1 RP/unit.
• Minimum of 1 Gold Bar.  The greater the spell's affect, the greater the cost to cast.