What stats would you give to Indian Battle Elephants?

Personally? I'd give em increased attack speed.

Hp, Armor, Attack, Speed, And Discount are all taken. That leaves an upgraded version, or attack speed, or creation speed.

Attack speed would be good, quite strong in fact. Creation speed is weak for an expensive unit.

Imperial battle elephants would be cool as well.

BUT!

I think the best thing to do would give them Elephant Archers in the archery range. And make their new UU the Urumi. It attacked using a whip that dealt damage in an arc in front of them.

Although this would make them the first civ with 3 unique units. Unless you count the Tatars.