well it gets pretty stupid as it goes. the abyssal 5* literally shreds everthing and to progress its up to luck and rng enemy spawns. I've beaten stage 17 on first run to stage 18 now i've lost stage 17 around 9 times now? If they spawn either a FV or Jadgtiger your pretty much fucked as nothing will survive. If they spawn any artillery your also fucked as they'll one shot things with their skill.