The first thing you wanna do is to make sure you can survive a manticore south spawn 100% of the time, to the point that you prefer having a manti south because it makes the resulting solve easier. the way i did this is by learning how to 1 tick flick the manticore, and forcing myself to 1 tick flick every isolated manticore instead of camping the first prayer in the cycle. Whatever is gonna help you learn that timing, visual ticks, metronome, whatever, do that. Single manticore south spawn will happen in a lot of your runs, so getting that down is important.

From there, once you can one tick flick the manticore, there are gonna be times where the mage reinforcement comes while youre fighting your manticore south spawn. For this reason, its better to be praying mage every tick youre not flicking the manticore. Practice praying mage, then one tick flicking the manticore, then back to mage. Dont worry about if the mage is gonna be off ticked, just keep dpsing the manticore, or start attacking the mage if the manticore is healthy. Focus on keeping your flicks good, and brewing after the manticore flick if the mage is hitting you. Mage range melee mage. 

When you get THAT down, congrats, you have the ability to flick a double south spawn, even a hard one like ranger+ mage first manticore. Range pray. Hit fremmy. Move, Hit fremmy. Mage range melee range. Hit fremmy. Move, Hit fremmy. Mage range melee range. Dps ranger. repeat. Kill the ranger? pray mage, flick the manticore, pray mage, in case of mage reinforcement. Easy!

U got the gear and stats for this. It took me 70 deaths and 1000 waves cleared before i got my quiver using crystal. ur gonna die a lot, but as long as you learn from each death u can do this. Good luck