your bh slice...... it looks decent but you can make it better... Federer's is a great model to copy..
notice how he waits for the ball to come to him and really throws out the wrist as if he wanted to cut the ball in half.
imagine your upper arm, forearm, racket face all on the same plane, and you are gonna throw this heavy plane downward and forward at the same time.
the downward throw will help maintaining the face angle, while the forward part produces penetration.
indoor court, a good slice will be just as penetrating as the topspin drive.