The Culling

justintime is right about constantly moving. I'd get flanked if I stood still with multiple enemies! Thank you, Justin! Personally I always backed up from them because them hitting you in the back gives them extra damage. When trying to dodge shooters, I'd run left and right without aiming to move faster.
I also used DraKeN9nE's method and it worked well for the 1-2 punch, block. Thank you DraKeN!

A little bit of luck went into it. I had a couple of times where at the very beginning the Mandroids were standing still especially if they were across the arena and didn't see me or something, they'd stay there for about 3-5 seconds. I took my bow/gun and shot them as soon as I could. I don't think the arrows are affected by gravity, so I shot them head on even with the distance. With that distance, when melee Mandroids started running towards me, I'd shoot them again and then switch to the melee weapons. I tried not to horde...hoard?...hoard the good stuff because I was nearly to the last wave...consistently killed 46 and died for a bit. My tactics against bow Mandroids shooting at me was to rush them safely. Strafe diagonally at them instead head on if they're really far from you otherwise you'll take a hit. Rush them, rev up your hit and get them when they stand still. They generally ran away from me with their backs to me!

Every chance I got, I would buy something from mystery. The armor and the boosts helped so much and if you got a lot, save them, leave them on the ground near either the recycle area or the mystery box. I healed if it I got lower than 60 to be safe.

Getting the achievement took me 3 sittings! 2 hours of practice the first 2 sittings and today, I did it for an hour. =] Yay!

I found that the 2 or 3 Mandroids ganging up against you can hit each other! That was nice, but it's still a cluster. With the 2, I'd try to focus on wiping one out as quick as possible, never letting my back turn to either. Was difficult. I killed 49 and then died, but got the achievement because of that bug. I didn't think I could do it. Technically didn't, but I'll take it. =] I'm not a skilled gamer, so it worked in my favor that this game's mechanics weren't super complicated.

I hope everyone's experience is good, just practice and stick with it. Good luck.

Message me if you have difficulties and let me know what your experience is! Maybe I can help.

Going to throw in some developer logic for anyone struggling. The AI in this game loves to get itself stuck in loops of what it thinks you’re going to do. If you walk up to an enemy and hold block while backing up, 9/10 times they will blindly swing at you and get stunned. Hit them with a full charge attack and repeat, easy pickings. Anyone with a ranged weapon, run up to them as fast as you can while dodging bullets/arrows. The AI will always pull out their melee weapon when you get too close for comfort and you’re back to your rinse & repeat cycle. Make sure you’re gathering FUNC from recycling their items! Your ideal scenario should be to have 2-3 medkits in your inventory, a strong melee weapon (I recommend trident, tier 4 due to range/damage) Using this method I came up with above, I completed Advanced Survival Mode in one try with my only prior experience being the normal survival mode. (2 plays on normal and 1 advanced) Good luck. I’m available to chat if clarification is needed.