So, I am just a random player in Pixel Gun 3D and I guess people need to know an effective strategy for Arena mode. Now I know that not everyone will agree with this strategy but just bear with me, I know what I'm doing.
Something that a player might normally struggle with its ammo consumption. What I do is on the first few waves (1-5), I use my Backup weapon. This means that on later waves, I have more ammo for my Primary weapon. See, I use the Dual Shotguns, which means I don't have a large clip. You can use whatever you want when it comes to secondary weapons. It really doesn't matter. Shoot all monsters that appear on wave 1-5 with also gathering them all up into a group and using a Grenade to finish them off.
The waves that I struggle on are the later waves (10-20). Using a Primary weapon is very recommended as the monsters grow more and more aggressive. Explosives are also recommended. Melee weapons should not even be touched as the monsters attack more quickly and they do more damage. But some melee weapons help you move faster, so you can use them if you need to run away.
Ranged monsters are very hard to deal with. As soon as a ranged monster spawns, kill them quickly as if there is too many of them, the projectiles will most likely hit you. Using Sniper weapons are recommended, as they do a decent amount of damage.
If this article was helpful, please let me know. If you want to edit this article, please let me know. Thanks for reading! (Writer is Electability).