Guys what you wanna aim for in lvl 24 is a good first shot which for me cleared out the top 2 tiers and positioned the 3rd for an easy kill. Just keep retrying till you get a situation the shifting of upper-most tier causes the building to sway and squash the 2nd tier which then causes it to sway again and cave in =P
i honestly think the kong challenge was a joke. just get 1 apocolypse cannon and 3 blasters... upgrade the damage and 3 fire speed on the 3 blasters, and get the reload then health for the apocolypse