So yeah Proving Grounds are kinda fun in my opinion only problem is you have to wait like 80 minutes till it gets challenging... Wave 80 at 7:40

Note these are the tactics i used, they might not be perfect especially wave 9 but they worked best for me.

Guide
:
Recommended Glyphs: Regenrative magic, Pestilence, Icebound Fortitude
Recommended Talents: Rolling Blood, Aphixiate, Blood Tap. Remorseless Winter

Basics for all waves: use AMS and IBF to let orbs explode without getting stunned whenever you can.
Soulreaper is mandatory. if you kill something while it has soulreaper you get a big hastebuff what isnt bad or you can make it finish the last 25ish % whats also awesome.
on almost any wave mobs look too the entrance use that for positioning (i put a blue marker to make it easier too see)
Stunned Big adds cant make their shield.
Banshees have to be focused instanly


Waveguides:

Wave 1: Dot the adds in the middle, move instantly outside and kill the Mantid with help of their orbs (use Soulreaper below 35% and just move to next one)

Wave 2: Dot the Mantid and spread diseases, Instantly go to the Healmob and kill it as fast as possible, use first orb for the healmob second orb for one of the big guys and third orb for banshee

Wave 3: Remorseless Winter, DnD + Disease Spread GG

Wave 4: Dnd so you hit 3 target before phase, Dot Mantid spread diseases and kill one after one of the Big Guys, dont forget the Banshee and kill her with help of the 3rd orb

Wave 5: Dot everything, Grip the monkey stun and kill it fast, kill healer, use all cooldowns at about 32 sec left. place DnD right before banshee spawns at 30 sec and nuke her, save runes till sha shield is gone, nuke and dont forget soulreaper

Wave 6: Kinda easy Dot in the middle, Spread diseases, nuke one healer and then other one. just make sure they dont heal.

Wave 7: Dnd before phase, Grip stun and nuke monkey too the middle, spread diseases, use AMS for both first orbs and get the mob in the middle + monkey + 1 Mantid in amber, nuke the ambered mantid and let dots finish off the other 2 ambered mobs. use the other mantid orbs for the rest.

Wave 8: Hard. Dot healer, spread diseases nuke till 48 secs left then take berserkerbuff, first banshee spawns nuke her then healmob a bit. at 30 sec next banshee spawns make sure the healmob is still alive at that point so you can spread diseases. at 25 sec another banshee spawns so Dnd at 31 secs helps for both.

Wave 9: Hardest Wave havent really found a perfect tactic yet. I use ghoulstun for the monkey instantly dot it spread diseases and grip it to one of the other adds aphixiate it and kill it as soon as the first orb comes. then nuke the add in amber. use 2nd orb for the big add and 3rd orb for the banshee. Even with unholy frenzy this phase was always very close for me.

Wave 10: Easy, Army at 41 secs, berserkerbuff + gargoyle at 30 secs and nuke when shield is gone. 1,9 mill soulreaper crits ftw.

After wave 10 you have 15 secs to rest. you can use that to eat bufffood after wave 60.

Altogether i can say there are only 2 hard waves 8 and 9. Im not 100% sure myself where to use unholy frenzy and where the berserker buff.
I hope this guild helped some people and feel free to ask any questions

songs:

S.S.H. - Ys 1 - Palace of Destruction
S.S.H. - Sledge Hammer [Lost Child]
S.S.H. - Pegasus Illusion [Kidou Senkan Nadesico]