Besides being able to play friendlies with them, human beings are also great tools for specific practice situations! You can give them instructions and they will also benefit from the practice.
Spacing is one of the most fundamental aspects of Super Smash Bros. Melee. It can be summed up in simple terms as ‘knowing where and when to place your moves.’ This knowledge comes with experience, knowing your character’s moves and how long their reach is. But you also practice this mindfully, specifically with two people.
One of my favourite training regimes with new players to illustrate spacing is by picking Marth vs. Fox. I will Nair in as Fox and their task is to dashdance>grab me. While it sounds simple, it’s not as easy because you can mix up how early or late you do it. What this does is teach someone the concept of effective range. At what spacing do you have to dashdance as Marth vs. Fox to be able to react to a Nair and still be in time to punish it.
Practicing things like this is incredibly important, because these are situations you might encounter at your weekly tournament against that Fox that you hate. Besides being a simple practical exercise, it’s also practice in the whole concept of spacing. This can be extrapolated to every character. How far away can I be to safely do my moves?
Another exercise I’ve always enjoyed (and still do myself) is Falco’s Up-tilt wall. This is one of the most frustrating moves in the game and a Falco spamming this move feels untouchable until you take a moment to just actually look at the move. Just trying to get inbetween Up-tilts is a good exercise for newer players to practice their timing. If it proves very easy to do, you can mix it up with auto-canceled Bairs and Shines in between Up-tilts.
My final example is trying to Up-air or Up-tilt someone coming down from above as Fox. If they just drift down regularly, this shouldn’t be very hard, but if they mix up with fast-falls and aerial drift, it becomes much harder and requires fairly good timing.
All these exercises share one common, crucial aspect. Every single practice routine revolves around actively looking at your opponent. After you get tech skill down and can control your character, this is absolutely the most important thing to work on. Many new players have a problem with looking at their opponent and actively distinguishing what moves they are throwing out and what their ranges are. These exercises can hopefully help with that. Next time you sit down with a friend, maybe take five minutes out of your friendlies session and try to grab Fox’s Nair a few times, taking turns. Or even better, make your own exercise!