Fused Kyurem's stats and some moves are changed.
Black Kyurem's defense goes from 90 to 100, and gets a whopping 170 Attack Power. Plus, Black Kyurem also gets to learn Freeze Shock which is a two turn move with 140 Physical Power than can paralyze the opponent in replace of the move Glaciate, which only regular Kyurem can learn at Lvl 50. Pressure is replaced with Teravolt.
White Kyurem's special defense goes from 90 to 100, and also gets 170 Special Attack Power. Instead of Freeze Shock, White Kyurem will get Ice Burn which is the same as Freeze Shock, but deals Special Attack damage, and also has a chance of burning the opponent. This move also replaces Glaciate. Pressure is replaced with Turboblaze.
I did use the sprites from this website.
Here is the link to Kyurem to see for yourself: http://pokemondb.net/pokedex/kyurem