Sky City Survival to Wave 30
Start on Wave 16, Use Upgrader Jester to upgrade stuff. Upgrade the three 6DU Buff Beams at Middle Crystal to Three Stars as soon as you can.
Point DST's at Number Markers on Map.
For North and South Crystals, it's OK to upgrade the 4DU Buff Beam, but only to One Star! (Do not upgrade to Three Stars, nor upgrade the Auras and Traps here at all).
After Wave 20 I usually switch to a DPS/Boost Monk (Tower Boost is nice here) and a Summoner with App/Huntress Guardians, parked on top of the LT's.