Perhaps they would be simpler to implement as a fortress expansion only? This way, the trolls will never have to move and just lean on their hands all the time (effectively, they will be decorations for the catapult on their backs). If possible, one can take this a bit further and allow the trolls to swing their hands and attack troops that come near them. This way it can be the ultimate expansion - being able to attack catapults/archers at a distance and melee troops at point blank and thus, effectively defending the fortress against a variety of attacks.
Edited by ELB27, 11 July 2015 - 06:52 PM.