1. From level 1 to 4, focus on only farming GOLD and avoid experience. The more gold you have the more rerolls you can have to make sure to get your chosen gun as a second pick. And it's important to get it as a second pick so you can start leveling it up as soon as possible, while the pool of guns fighting for upgrades is smaller.

2. At level 5, reroll until you find your chosen gun. If run out of money and don't get it, it's time to restart since you only invested 2 minutes into this run and it's very cheap time wise to restart.

3. From level 5 to 15 your pool of gun is only 2, so you really want to spend every gold piece to reroll and find more of your main gun's upgrade. It will be harder when you have 4 guns to get upgrade for your 1 specific gun, so use those early levels to focus as much as possible on the main gun.

4. Same from 15 to 25, you're still having a pool of 3 guns instead of 4 so your chances are the best, i'd still use every available gold to repick guns until i find the main one.

5. Level 25+ ok now the pool of guns is the largest, so you want to have a more balanced approach, feel free to pick up complementary stats so you can survive and thrive up to stage 5. Now is time to pick up that mining speed, hp, move speed, and anything else that might help you kill faster and go farther.

6. Leveling up! Prioritize your main gun, rerolling into your main gun, and worst case scenario pick up nice side upgrades like pick up range (aim for 150-200%), mining speed (aim for 30% max but you can definitely make it with the base 16%), and mostly critical chance and the main stat that helps your main gun thrive, since we will mainly be killing with this one gun you don't care about upgrades or stats for the other 3.

- Again you want your main gun to be picked as a 2nd choice, else restart. Your odds are a lot worse if you pick your main gun at the 3rd or even 4th one.

- Farm the map and the minerals and try to get all the gold and nitra, even from the loot bugs. In other words don't neglect the mining in favor of farming xp, they are both important. Remember that between stages you can reroll for cheap, 5 gold 7 gold 10 gold, that's a lot cheaper than in mission rerolls and it gives you a pool of 5 choices instead of 3 so it has a higher chance to hit your main gun's upgrades.

- Unless you have a great overclock, you can salvage the one at 6 and/or 12 for an extra level. You might miss the level you want by 1 or 2 levels, so this might actually matter. Also because salvage guarantees a legendary, you have like a 20-25% chance to get a +3 level upgrade, which would be a big help. You should not need to salvage the final overlock at 18, but if you're struggling to hit an achievement it might give you the final levels you need to hit it. And remember if you salvage all 3 overclocks, that's 3 more levels and a bigger chance to get a bonus +3 from one of them, don't sleep on this if you're having a hard time getting the achievement.

- Keep all your gold to reroll into your main gun upgrades, and keep all your nitra to level it up between stages too. If you're out of gold for rerolls in between stages, keep the nitra for the next time you are between stages to try again to get your main gun upgrades. Just be stubborn, it pays off well for this challenge.

- Keep at least around 22-36 gold by the end of the stage so you can do at least 3 rerolls between stages, one at 5 7 10 and then 14, to try and dig for more of your main gun's upgrades. The more nitra you have stockpiled the more gold you want to save for the shop in between stages. Something like 20% of whatever nitra you have as gold is a rough but good rule of thumb.

- You don't want to be picky with the 3rd or 4th gun just pick whatever is best among the 3 choices. Since we will be boosting the 2nd gun to as high as possible, it should be enough to carry the game in terms of dps and the other guns are mainly support, so prioritize taking slow freeze and knockback or any synergies with the main gun. (Note: In a normal run, you want to boost 2 guns to 18+, so those will be your 2nd and 3rd gun, but in 1 gun challenges you are only boosting 1 gun this is why the 3rd and 4th gun are not very important, most of your dps is coming from the 2nd gun. The best you can do is pick a 3rd and 4th gun that benefit from the same global stats as your 2nd gun, this way they will get stronger with it as you pick stats that affect it.)

If you enjoyed these tips or want to see them in action, feel free to find me on Twitch, nickname Drakenkin

https://www.twitch.tv/drakenkin

I only stream hazard 5 and I am currently doing a win streak challenge using a different build everytime, current streak is 10 wins. I also always explain my decision making so if you're still learning about the game i believe you will benefit from watching.