First of I'd like to say that this mod is truly one of the best I've played. I've had more fun with Minecraft with this mod and the Alex's mobs mod than I think I've ever had with base minecraft. However, I still noticed some issues with the mod that I believe would make the mod even more fantastic if fixed or tweaked.

First off, I feel like having the biomes generate outside of a X: 5000 and Y:5000 zone is a little too far. I know these biomes are supposed to be ultra rare, but I feel like travelling to my first Magnetic biome at X:-5000 and Y:8850 is a little too much. I think that every first cave of the new biome should be within or less than 5000 or negative 5000 from spawn in order to make the exploration process less tedious, especially if its the first map you've made for the biome.

Next, I feel like some of the new enemies within these biomes either have attacks that are insanely strong and fast, or have insane range with stong damage. The enemies I mainly refer to are the Teletor and Brainiac. The Teletor though the concept is cool I feel has way too much range. This, alongside its notable damage, small stature and ability to fly makes it the toughest enemy of the biome easily, even compared to the Magnetron. The only thing I suggest fixing with this enemy is its damage output, and its range. If that means cutting the range of the Galena Gauntlet then thats ok, as long as it makes these enemies less frustrating to deal with.

Next is the Brainiac. The brainiac's damage and speed are fitting for its dangerous environment, though slowing it down just a notch would make it easier to not get overwhelmed by it. The biggest issue I have is the tongue range of the brainiac. The brainiac should have a shorter range with the tongue.

Next is an issue I have with the acid. The acid biome is truly the most dangerous biome I've witnessed with this mod, mainly for the fact that there are dozens of pools of acid to destroy your materials and gear. Though I understand it destroying the overworld/ other biomes gear, I feel like it should not apply for the Hazmat suit and Radgill. These items are not only from the acid biome but outside of their item form they are perfectly immune to acid. I feel this should also logically apply to them in item form as well, and have them float to the top of the acid for the player to grab.

Next, the raygun should have more charge to it, even if just a little bit. The ammo it uses is very expensive to make (Blaze rods specifically). If you made it so that either the charge was set for a max of 2000 or that when you crafted the uranium rod it made 2 instead of one then it would make the raygun just a bit better, and less material consuming.

Next is the Abyssal chasm. There are only 2 issues I mainly have with this biome, that being how rare it is to recieve the Sea Staff and the damage output of the Sea Staff. The Deep One Mage should provide the Sea staff earlier than it does now, since in its current state, the weapon does not feel like its worth the thousand block trip to the abyss, and the dozens of pearls used for trading with the mage specifically to get it. I would understand the rarity if the weapon was powerful, however it is not very strong in the damage or durability department. For example, when I used the weapon against a Magnetron, it took a very long time to kill it, and when it was dead, my staff which hadn't been used once until that moment was at nearly half durability. If you want the weapon to stay at that rarity within the trade, then buff the damage output, and durability of it. If you want to change the rarity so that its easier to obtain then it would make its current damage and durability less of an issue due to its easy obtainability.

Next I would like to see the Hologram projector and the Holofilm adjusted so that if the projector is destroyed, it also drops your previously inserted Holofilm, so you can use it again instead of having to make another one.

Outside of these issues, I have been loving every moment in these biomes. I personally think that the Primordial caves is perfectly crafted with no issues, and the rest, though as listed have a few issues, still feel, look and play phenominally. The only cave that I haven't been to yet is Forlorn Hollows, so if I pick up on any issues or suggestions I have with it I will drop them here.

I especially agree with the Teletor's and Brainiac's ranged attacks, it's actually crazy how far away they can be and still hit you.

This is rather hard to read as a large wall of text - I'd just like to suggest formatting your suggestion in a more digestible manner.

EDIT: Much better, thanks! That should help your suggestions receive more interest.

Brainiac tongue attack should be just a special attack imo, like grab or pull you from a far or when player pillaring .Idk why it becomes a secondary basic attack when their punch attack is already enough (if im not mistaken they still do this even when theyre 1 block close from the player, might be misremember it)
Pretty sure the trait/point for hazmat is making player resistance from radioactive, not acid.Idk if radgill is much of an issue, but if its changed its good ig

Brainiac tongue attack should be just a special attack imo, like grab or pull you from a far or when player pillaring .Idk why it becomes a secondary basic attack when their punch attack is already enough (if im not mistaken they still do this even when theyre 1 block close from the player, might be misremember it) Pretty sure the trait/point for hazmat is making player resistance from radioactive, not acid.Idk if radgill is much of an issue, but if its changed its good ig

The reason I brought up Hazmat not getting destroyed in item form is because even though the main purpose of the suit is indeed to negate radiation, you can also swim in acid with it, and not have it get destroyed or deteriorated like all the other armor sets. Because of this, I felt it would be logical to have it be invunerable to acid in item form.