Make the 1st Archer's "arrow rain" chargeable:
1st level: Multiple arrows fall - a little range (like the current one) 25% mana
2nd level: Rapid Multiple arrow fall - 5 times more range, more arrows 70% mana
3rd level: Forest Archer Military Barrage - somewhat like Gaara's DvA (Tre Pac knows), continuous, 100% mana