Try as hard as possible to only use up b when absolutely necessary. It is easily punishable by most characters if the player knows what they are doing. Try to airdodge to the stage and things but still remember to mix it up.
Chrom's Up-B is extremely similar to Ike's Up-B in terms of looks and properties. It goes a great distance in terms of height, but it has one of the worst horizontal movements in the game. Use this move wisely when trying to recover
Roy's Up-B has been buffed from Sm4sh. It now has even better horizontal distance and it goes a little higher than it did in its predecessor. Also, while using this attack you maintain all of your momentum.
Chrom