The one big constant balance issue.

[Arcane Azmadi]

The game has a number of balance issues both big and small, but there's one overriding one that dominates all the other, which has been present since the earliest version of the game. And that's that 2 of the passive upgrades, specifically the Pneumatics and the Gravity Retractor are literally mandatory in almost every single run.

Pneumatics, which boosts your speed, is self-explanatory, while also being the only one with exceptions. The Titus (the mech which gains speed with every level-up, as well as being the fastest by fault, tied with the Drake) is normally the only mech which can pass on the Pneumatics, which is ironic because the Titus' other gimmick is that it has more passive upgrade slots than almost any other mech (tied with the Striker at 5) and therefore could easily sacrifice one to fit the Pneumatics, compared to the Dozer which only has two passive slots and consequently can only take the Pneumatics and Gravity Retractor. The Drake (which, as mentioned, is tied with the Titus for highest base speed) can just about get away with not using it, largely because of its overwhelming firepower, and the Benedict can hypothetically get by without it if you keep the eggs going, although both will still simply play better with it. Without the speed upgrade, every other mech is simply too slow to stay ahead of the massive hordes that start running you down, and will eventually be overtaken and torn into scrap no matter how good your weapons systems are. Some mechs like the Arachmech are so painfully slow that even playing at them all is an agonizing experience until you luck into Pneumatics. Additionally, and this is something Pneumatics shares with the next point, the faster you move the faster you can reach dropped crystals and the faster you level up. Since levelling up is the #2 priority in this game (after #1: survive), Pneumatics is not only an essential survival tool, but an essential level speed multiplier.

Unfortunately, Gravity Retractor is even more essential than Pneumatics. This one is even simpler: the higher your gravity, the easier you collect crystals, the faster you level up. The mech with the lowest gravity (ironically the Titus again, at a pitiful 4) has to literally stand on a crystal before it's able to pick it up, and even the one with the highest (Runner RX, capped out at 18) benefits so much from the Retractor that not taking it is foolishness. When your late-game Dreadnought weapons are blowing up enemies all around you all over the field, without the Retractor you might be able to pick up maybe 10% of the crystals they drop if you're lucky, even fewer if you're desperately kiting away from a ravenous horde trying to run you down, leaving all the crystals behind. A maxed-out Gravity Retractor doesn't just double your leveling speed, it quadruples or quintuples it, and since enemies aren't civil enough to wait around for you to level up at your own pace before swarming you in gigantic hordes, levelling speed is life. This isn't a point I'm even willing to debate on: if you don't take the Gravity Retractor, you suck at the game. This is an issue shared with the game's genre leader, Vampire Survivors, as well- while the Wings (that game's speed increasing passive item) are significantly more optional than this game's Pneumatics because of VS's stronger weapons and slower enemies, you basically have to take the Attractorb to be able to level up efficiently. I assume it's an issue that applies to every game in this genre, although I haven't played many others yet. However it think this game has it even worse since every enemy in this game drops crystals rather than only having a chance to do so (in exchange for the actual exp gain from crystals being lower), meaning you have to collect more individual crystals to level up.

What can be done about it? Not sure, really, but I have a few ideas- slowing down later-game enemies so you actually have a chance of staying away from the ones you can't vaporise even without Pneumatics would help. The bigger adjustment, I think, would be significantly increasing the base gravity of all mechs and, oddly enough, nerfing the Gravity Retractor so it merely enhances your attraction range rather than quintupling it (and consequently your leveling speed). Also, I suggest adding more permanent Perks to the game than just +4 max AP and +2 damage- the ability to pick a perk to gain +1 gravity would go a long way towards making the Retractor less mandatory than it currently is.