What exactly is the gunner update going to bring?
New weapons and armor as well as reworked damage. (poor Zeddy is gonna have to rework everything)
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What does this mean for the game?
More choices.
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Will this affect the current Chaos Cloak/Brandish/SSB metagame?
Aside from new pulsar/blaster choices not much. (maybe antiguas)
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Will anything become useless?
Your PVP catalyzers won't deal damage anymore, just tag recons (dear god we have so many recons that this is perfectly reasonable and we need something else that makes their cloak even more useless) #sarcasm
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In all honesty the update will bring new items to the game, how they fit in is determined by the current metagame. The new CTR boosting armor will end up being a good first gunner set for FSC but much like other armors it will most likely be abandoned during the endgame for something like Chaos Cloak (not to hate on CC). New Damage types on fast guns means they will fit into the current metagame by giving more ranged choices to pair with Brandishes. Slow guns (like usual) will most likely get ignored. The new pulsars may get ignored just because shock status is "the best status in the game", they may find some use in PVP where most people have UV rolled to buff their shock resist but other than that I won't expect much. New damage types (piercing) on the more mobile guns will mean we have better choices when it comes to combating certain enemies.
While the gunner update will diversify everyone's choices and loadout I don't see it as revolutionary as some tout it to be.
Of course I will be waiting for the day it comes out but I just don't expect too much to change.
I don't think that we are supposed to talk about it on forums. If you are interested then you can check out the modles in SpiralSpy or the hidden in-game files in the game itself.