A ladder event is a scheme where you get promoted/demoted in a list of players based on your match performance with the others. However, there are rules as to who you can challenge which generally restrict you to those immediately above you. How many players above you is a setting that the event organiser makes, and is generally a small number - say 3 or 4.
However there are some specifics as you may find that you can invite more than this. Here are the specific circumstances:
- If you've entered the event for the first time you will be "unplaced" in which case you will be given the opportunity to invite anyone in the ladder whose MMM internal player rating is below yours. If MMM has not been able to rate you yet (you may be new to MMM), you are prompted for an indicative rating in the bookings centre - please respond to that.
- Generally, you'll be able to invite anyone above you in the ladder so long as they are either within distance as per the organisers setting or have an MMM internal rating less than yours. The latter rule provides for the scenario where a good player joins a ladder and can skip the lower echelons of the ladder.