There is a world somewhere between reality and fiction. Although ignored by many, it is very real and so are those living in it. This forum is about the natural world. Here, wild animals will be heard and respected. The forum offers a glimpse into an unknown world as well as a room with a view on the present and the future. Anyone able to speak on behalf of those living in the emerald forest and the deep blue sea is invited to join.
Like Bro Bear mentioned, killing a Rhino in my opinion is by far the toughest task. Even over a elephant, I think Rhinos being so massive and "armored" as well as low to the ground, its just a very hard animal to prey on. Even Lion prides more regularly prey on Elephant than Rhino, I would probably put Hippo up there as well.
Another Tiger predation animal that is amazingly impressive is the Asian Water Buffalo, its the 2nd largest Bovine and has horns larger than any other. There are a few images of tigers preying on them as well as wounds suffered by tigers.