Spell Level | Move | Morale | Cohesion | Defence | Melee | Charge | Missile | Special | Example |
1 | 3 | 6 | 2 | 10 | 2 | - | - | - | Animal, Small |
2 | 3 | 6 | 4 | 12 | 3 | - | - | - | Animal, Medium |
3 | 3 | 6 | 6 | 14 | 4 | - | - | - | Animal, Large; Elemental, Small |
4 | 3 | 6 | 8 | 16 | 5 | - | - | - | Animal, Huge |
5 | 3 | 7 | 10 | 18 | 6 | - | - | +2 Defense to non-magical attacks | Elemental, Medium |
6 | 4 | 7 | 11 | 20 | 7 | - | - | +4 Defense to non-magical attacks | Elemental, Large |
What is the chance of control? Summoning high-level nasties from the shadow world shouldn't be safe for anyone - and powerful monsters may be far more interested in following their own plans than fighting some-one else's battle, they might not leave on cue either...
If you want a spell to have duration, then I'd suggest giving it maintenance cost to keep it in-line with 'normal' armies which have muster and maintenance costs.