1.16.5 My code not working

Is it returning output to the console?

 

Did you add @EventHandler before the event? It would look like this:

Code (Text):

@EventHandler
public void onMobSpawn(CreatureSpawnEvent e) {
        if (mobPot) {
            LivingEntity mob = e.getEntity();
            Random rand = new Random();
            mob.addPotionEffect(new PotionEffect(potions[rand.nextInt(potions.length + 1)], Integer.MAX_VALUE, 5));
            System.out.println("Mob is potioned");
            Bukkit.getConsoleSender().sendMessage("A mob is potioned");
        } else {
            System.out.println("Mob not potioned");
            Bukkit.getConsoleSender().sendMessage("Mobs didn't get potioned");
        }
    }

Also, you need to register the event.

 

Hello,

You probably forgot the @EventHandler annotation.
Also, make sure you registered your listener.

A complete tutorial about the Event API is available here: https://www.spigotmc.org/wiki/using-the-event-api/

 

Ur welcome. Also, you need to make sure your event is registered.

 

You can get a list of potion effects using LivingEntity#getActivePotionEffects(). You might need to iterate over them using a foreach loop.