The Proximity Detonation Explosive Gel upgrade is required. In Challenge mode, choose Rumble In The Jungle and fight through the first three rounds, conserving as much health as possible. In round 4, do not engage the Titan until everyone else in the room (other Arkham inmates) has been put down permanently. Do not use a Batarang -- if you hit the Titan with it at all, it voids the achievement. Quickly switch to your Explosive Gel and wait for the Titan to charge at you. Watch out since there is always a chance he will throw a dead body at you first. Dodge the charge, then set one of your own (meaning spray the floor with Explosive Gel; it is best to do it rightafter he rushes at you and make sure you let Batman completely spray the gel). Stand over the area you sprayed if possible. When the Titan charges again, evade and you should hear a loud bang. The explosion does not take much health off the beast at all, but it does not matter. After he takes one big blind haymaker punch move in, continue hammering him with attacks. You can build up a good twelve to fifteen hit combo on him before Batman delivers the knockout blow, earning you the achievement.