TL;DR:
This is based on AI enemies, not real players
Pick three high-base-statted Pals, fully condensed, max IVs, level 64+, all damage passives
Get Vortex Beater (Terraria weapon), and 2k+ Assault Rifle ammo
Which Pals to Use for Arena Master Rank
It is likely possible to beat Master Rank with lower-leveled Pals, and worse-statted ones at that. I think the most important part of the strategy is stunlocking the enemy trainer with the Vortex Beater.
However, I’ll be going over the formula that I put together to chain Master Rank wins without losing.
This is the current team I use to beat Arena Master Rank:
Bellanoir Libero with 4* (fully condensed), max IVs, and level 65. Its passives are:
Musclehead
Siren of the Void
Demon God
Serenity
Bastigor with 4* (fully condensed), max IVs, and level 65. Its passives are:
Demon God
Vampiric
Serenity
Legend
Neptilius with 4* (fully condensed), max IVs, and level 65. Its passives are:
Diamond Body
Lunker
Serenity
Legend
I chose these three Pals because of the spread of the their typing, their strong Active Skills, and their high-base stat totals.
In case you didn’t know, there are hidden base stats that each Pal has, and you can think of them like a potential. For example, a fully-maxed Jolthog Cryst will never be able to do as much damage as a fully-maxed Bastigor, because the Jolthog Cryst’s base stats are lower.
So, if you’re looking to form a strong team, I highly recommend picking late-game Pals like Frostallion Noct, Necromus, Frostallion, Jetragon, etc.
What Weapon to Use for Arena Master Rank
The weapon I’ve found the most success with is the Vortex Beater. It’s a weapon you have a chance to get from the new Tides of Terraria dungeon. It’s definitely worth the effort to get it.
It functions similar to the Assault Rifle, with two major differences: it periodically shoots homing rockets that stagger enemies like a Rocket Launcher would, and you never have to reload. Yes—you literally never have to reload. That combined with the fact that it constantly spews out rockets at a faster pace than the Rocket Launcher can, means you can effectively stunlock enemies.
A great thing about the Arena is that any ammo you’ve used in a fight will be returned to you after the fight. I think the game likely just takes a mental note of whatever you have before you start the fight, and then resets you back to that state after you finish. So, other non-ammo consumables are probably replenished too, but I haven’t tested that.
The ol’ four Gobfin strat doesn’t seem viable in Arena. I’m not sure that you gain the passives from Pals that aren’t in the Arena battle. Even if you do gain those passives, the damage that you do will be nothing compared to what the enemy trainer will be doing. That’s why your main goal in Arena is to stunlock the enemy trainer.
How to Stunlock Enemy Trainers in Arena
Right on round start, I use Bellanoir Libero’s partner skill on the enemy trainer’s Pals, and then I don’t stop shooting the enemy Pal trainer until they or their Pals are dead.
It can be that simple. It’s boring, but effective.
This works on every single enemy trainer that I’ve faced so far. As long as you are firing your Vortex Beater at the enemy trainer, and those rockets are hitting them, they won’t be able to do anything except bounce around.
The most dangerous enemy Pal trainers are the one with the Rocket Launcher, and the ninja one. The Rocket Launcher one shoots very slowly, but when it does get a shot off, it’s going to do a TON of damage and may even one-shot one of your Pals. The ninja is dangerous just because of how mobile they are. It can be challenging to keep your Vortex Beater firing at them when Pals are jumping around and breaking your line of sight. And as soon as the ninja isn’t stunlocked, they’ll dash to attack one of your Pals.
Optional Items to Speed up Wins
I also choose to bring Attack Support Whistle, its +1/+2 variants, and the Defense Support Whistle +2. All the Attack Support Whistles will increase your Pals’ attack by a couple hundred, and the Defense Support Whistle gives them a little extra tankiness.
There’s also the Terraprisma, a sword from the Tides of Terraria dungeon. If you equip it, and swing it nine times, nine swords will be summoned behind you like a cape. When you’re in battle, those nine swords attack whatever you’re fighting, even if you’re not currently using the Terraprisma. All you have to do is keep it in one of your four Weapon slots, and you’ll get nine swords of additional damage.
The swords don’t do a ton of damage with each individual hit, but they attack very quickly, and there are nine of them, so the damage adds up.
The best part—and this is pretty silly— is that you can summon the nine swords before you start an Arena battle, and you’ll take them into the battle with you. I haven’t done any PvP in Arena yet, but I’m assuming this feature makes it a must-include for the sweatiest Pal trainers out there.
The last optional include isn’t an item, it’s Bellanoir Libero’s Partner Skill, Nightmare Stare. Bellanoir is an all-star for many reasons, but mainly because she’s got the highest attack potential in the game. In addition to that though, you can activate Nightmare Stare while firing your Vortex Beater, and there’s no hesitation in your shooting.
There are likely other Partner Skills that function the same way, but Nightmare Stare is one of the strongest Partner Skills on arguably the strongest Pal in the game. If you’re looking to min-max as much as possible, consider adding a Bellanoir Libero to your team to fire off her Partner Skill without losing any DPS.
Rewards for Arena Master Rank
When you beat Master Rank for the first time, you’ll get 100 Battle Tickets. For each win after that, you’ll get 10–20 Battle Tickets and 1–2 Exotic Spheres. The 10–20 points seems to be random, and doesn’t seem to be based on how well you do, or how fast you complete the battle. You’ll also get +75 points to your Arena ranking for each win.
In conclusion, bring strong Pals, and let them solo the other Pals while you stunlock the enemy trainer with a Vortex Beater. As long as your Pals are good enough, you’ll win every time, and quickly too. Each battle will take three-to-five minutes or less, and that includes menuing and opening cutscenes. Also, it’ll take 75–150 matches to have enough points to unlock a legendary schematic. GLHF!