The original biathlon is a combination of cross-country skiing and shooting (with a rifle). Basketball biathlon is a combination of dribbling and shooting (with a ball). In the original biathlon athletes use two shooting positions (standing up and lying down), we use bank shots and free throws.
Set up two adjoining basketball courts (i.e. 4 baskets in total). Set up a circle of cones in both middle circles.
1 player stands with ball under each of the baskets. The players take five bank-shots from somewhere around the low or middle block (you can have another player helping out as a rebounder/passer). If the player hits all five shots, she takes the ball out of the basket and sets off on a dribbling course around both of the courts until she reaches her own basket again. Then she shoots five free throws and repeats the same procedure, then another five bank shots from the other side of the lane and finally another five free throws.
The fun starts when a player misses a shot. For every missed shot in a series of five, she has to do a penalty lap around the cones at the nearest middle circle (thus three laps for three missed shots etc.) and then set off around both courts. the biathlon ends when a player had completed the penalty laps for the last series of free throws, then another 4 players can start.
I find that a time of 2'30'' - 3'30'' for the whole thing is ok for my team (girls 12-14). Depending on the level of skill faster times can be done.
4 or more
Emphasize concentration on the shots. Shooting five quick shots and having to do four or five penalty laps is always worse than taking a bit of time and having to run no penalty laps.
if you have 8, 12 or 16 players, you can make this drill into a relay.
Shooting when tired
This basketball drill is licensed under a Creative Commons License. This drill is from Pål Degerstrøm at www.degerstrom.com/basketball.