Produce a high volume of finishes from genuinely different service, taken under fatigue. Players adjust their body and technique to whichever ball arrives rather than grooving one shot.
Set three mannequins as a central wall with a fourth behind them, a server on each touchline and one centrally. Put a keeper in. Servers deliver in rotation, alternating long wide balls with short central feeds, and the finisher takes each as it comes: the wide ones first time from around twelve metres, the central ones after a short carry from fifteen to eighteen. Keep six balls circulating so a delivery is always arriving. Change the finisher every ninety seconds.
Finishing sessions are usually run fresh and slow. A player arrives at the front of a queue, collects himself, receives a predictable serve, and strikes it well. He then walks back and waits ninety seconds. Almost nothing about that resembles scoring in a match.
Six balls changes the conditions rather than the technique. Deliveries arrive every few seconds, so there is no time to reset mentally between them, and after a minute the finisher is genuinely tired. That matters because technique under fatigue is the only technique that shows up in the eightieth minute, and a session that never induces it never tests it.
Mixing the service is what stops the volume becoming mindless. A twenty metre ball from the touchline arrives with pace and has to be redirected first time; a nine metre central feed arrives slowly and has to be carried before striking. They are different actions requiring different body positions, and alternating them means the player has to read each ball rather than pre-programme a response.
The coaching job here is mostly about the servers. Left alone they fall into a rhythm, taking turns in a fixed order at a comfortable interval, and the finisher starts anticipating. Once that happens the drill has quietly become a queue with extra steps. Servers delivering out of order, without calling, is what preserves the reading element, and it costs nothing to insist on.
Save it to your private drills, then change the animation, adjust positions, swap equipment, or drop it into a session block. Or start from a blank pitch and build your own.