Korea coaches who work with amature club players have a system pretty consistent across different clubs.
With brand new players, it is almost 100% multiball. You would think after a few sessions, coach would progress player to newer stuff, but they stay on the same drill like a bloodhound dog until the player can do seemingly 1000 hits correct. When the coach does move up the player to something new, it is usually another multiball drill. Only time you see single ball is during the FH to FH warmup. When coach finally does phase in a single ball drill, it is usually the FH drive, then BH punch keep it on table and alive, FH Drive, BH Punch forever.
When player gets to be a decent div 4 level, coach does more and more single ball. Usually serve short to BH or FH, player bumps it back short or fast deep to BH corner, coach pushes long to BH and player either BH or FH opens, then covers a fast block to FH line, then tries (usually unsuccessfully) to cover the resulting fast block to BH corner. That is one of many drills. Some of the more explosive ones are BH flick to BH corner, step around FH, then crossover step to wide Fh, then another crossover to BH and back and forth as long as you can.
Even with Div 1 players, coach will still use some multiball, but it is maybe 1/4 of what they do. A couple multiball drills at that level are coach feeds a short cut, player steps in and flicks and coach gives you a fast ball at your crossover that you must recover and hit with a FH drive. Another multiball drill is a simulation of Falkenburg where coach keeps sending random deep cut balls to FH, crossover, and BH and player must FH loop ALL of these. Another usefull multiball drill is the block and counter drill. Coach stands close to net and machine gun fires lots of fast balls everywhere random and you gotta block, sometimes if you see it in time counterdrive for winner. Coach will feed it faster than you can practically handle, but that is what causes change in you to become faster.
