All messages, except the top welcomers message, support PlaceholderAPI. You can also apply placeholders for multiple players in a single message like this.
If you're using spigot you need to have PlaceholderAPI installed.
On bungeecord (PlaceholderAPI need to be installed on your spigot servers), you need to enable and configure it in the config:
# Enables PlaceholderAPI support
# Single - all servers receive the message parsed by the specified one
# All - every server parse the message by itself but, if PAPI is not installed,
# the placeholders will show in the message
# Server name for "single" mode (name is the one specified in the config.yml file of your bungeecord)
All messages and commands, except the welcome command and the top welcomers messages, can be single or random like this:
new-player-message: "single message"
- "a random command"
- "another random command"