Complex sentence: Danny grasps how insane The Shredder truly is after knowing his past, but he inadvertently warns him that the turtles have returned and they raid their home, but the Foot are ambushed as the group has already anticipated their attack.
Split into simpler sentences: Danny grasps how insane The Shredder truly is after learning his past, but he inadvertently warns him that the turtles have returned and he sends his men to raid their home. However, the Foot are ambushed as the group has already anticipated their attack.