Kingdom Rush

After beating the main campaign a number of additional missions will become available. The one you’ll want is “Ruins of Acaroth”, in the lower middle of the map. This is a 20 wave mission, ending with a huge horde of various orcs and trolls, as well as the mounted-on-a-mammoth boss Gul’Thak. After outlasting the horde he managed to get close to the exit. I held him there with the hero, a fully upgraded batch of paladins, and constant spam of summoned reinforcements. Tower fire from a mix of sniper towers and Wizard towers finished him off.