Use Bear Form ability, with the first unit being unable to move and the other one able of moving. The mana is triggered, when a unit is issued an order with no target and this order is "bearform", then add this unit to a Unit group. Another trigger will fire up, running every 1.00 second, that picks all units in that Unit group and sets their mana to (Mana of (Picked unit)) - X. Also, make a check, when the group is empty (Boolean comparison), turn off the trigger. Another check of whether the mana of unit is less than X will issue the unit to unbearform: Unit - Issue (Picked unit) to Night Elf Druid of the Talon - Night Elf form. Finally, when a unit is issued an "unbearform" order (String Comparison), remove it from that Unit group.