Giant on a Mammoth

It could be a rider like thing. It basically has two lives. It first fights in two life cycle.
First life stage is when it is still on the elephant/mammoth. (HP is twice that of a giant)
When the HP is drained it dismounts the dead Mammoth and proceeds with the second life stage.
Second life stage is when the giant dismounts the elephant/mammoth and then it starts it's rampage. (HP is 75% that of a giant however it's movement and attack speed is heightened)

As for the costs:
It should be worth 4000 Normal Elixir
And 1000 Gold (or not)
It should require a slot occupancy of 15 or possibly 20 give or take.

It's favorite target still is defensive units.

What is its DPS?

DPS could be like 1.7 times greater than that of the original giant. As for the heightened attack mode it could be as fast as an archer.