Axiom Verge includes more than just a wide variety of useful weapons. The game also touts a series of upgrades for protagonist Trace which allows him to reach new areas and thus find new items. Many of the upgrades are mandatory, but some can be missed by the less vigilant players out there.
One of the first upgrades in the game allows players to drill through walls. You never know what secrets you might uncover if you check every nook and cranny...
The Address (and eventually Field) Disruptor helps set Axiom Verge apart from other games in the Metroidvania genre. Shooting the disruptor at enemies glitches them in such a way that they're more vulnerable or not dangerous at all anymore. Keep shooting it at enemies to uncover some very creative glitches.
The Disruptor can also be shot at walls to uncover secret worlds or hidden areas. It's not always obvious where to shoot the Disruptor, so just be sure to check every room thoroughly if you're looking for most of the weapons and upgrades in the game.
Players can teleport through thin walls with the lab coat. Just double tap in a direction and hold the button to end up on the other side. A lot of hidden areas become available with this upgrade, so keep an eye out for one-block walls.
Players can now teleport through thicker walls (two blocks wide) in an instant. You no longer have to hold the directional button to end up on the other side, just do a quick double tap. It obviously helps with finding more secrets, but it's also a great way to navigate the environment or escape enemies.
The final coat upgrade makes it possible to break through blocks on the other side of a wall. That's in additional to teleporting through walls, just like the lab coat and trenchcoat. The red coat becomes available near the end of the game, and there aren't too many spots in which it's necessary to break through blocks on the other side of a wall. Nevertheless, it has its uses for players who want to find 100% items.
The Grapple Hook is an optional upgrade that allows players to swing across the environment, a la Bionic Commando. The combination of dashes and the drone teleport make the grapple hook obsolete at a certain point, but it does provide access to a few secrets earlier in the game. The controls for the grapple hook take some getting used to; remember that you can shorten or extend the hook by pushing up or down.
Press the triangle button to send out a small drone. The drone can reach areas that are far too small for Trace to explore, but the drone only has so much health. Players have to be careful not to let the drone die, otherwise it gets sent back to Trace and then there's a wait time for the drone to recharge.
Also remember that the drone can be thrown quite far. Combine Trace's teleport jump with a strong toss to reach very high areas that might otherwise seem impossible to get to.
Near the end of the game players come across an upgrade that adds a teleport ability to the remote drone. Press the triangle button to throw out the drone, and press it again to teleport to the location of the drone. It's arguably the best way to get around in Axiom Verge, and it opens up a bunch of new areas. Also, the drone teleport can be used to quickly escape enemies.
The Bioflux Accelerator makes Trace look like Doctor Octopus, but unfortunately it's one of the least useful upgrades in the game. It adds some tentacles to his body which shoot additional projectiles, but only at full health. Let's just say most players won't be at full health for most of the game. It's nice to deal extra damage every now and then, but in the grand scheme of things the Bioflux Accelerator doesn't help much.
The Address Bomb creates a huge glitch explosion, affecting all enemies in the area. It also affects the environment much like the address disruptor, and some glitched areas can only be accessed with an address bomb. Players can carry three at a time, and enemies often drop them in addition to health.
One of the coolest upgrades in the game allows players to input codes. Some codes translate notes written in other languages, while others open up secret passages. Good luck finding most of the passcodes in the game though, as they often reach Fez levels of complexity. Here's a fun one for free: input "JUSTIN-BAILEY."