There are 5 owls on the northern crystal and 4 on the southern one.
If you start on Wave 32, upgrade both buff beams before you begin. Upgrade the northern tower stack first, ignore the minions, give them maybe 1–2 ups, and then switch to the southern tower stack to upgrade it. Once both tower stacks are fully upgraded, join the summoners in split-screen mode (usually still during the wave)
Place one summoner with 1x squire and 1x huntress or speed poly on each of the locations marked in hint 2
Place a character of your choice on hint 3 with a Monk Guardian to boost the auras.
All summoners need resistances and some health, the fourth character is up to you.
If you start on wave 32, the whole thing takes about 18–22 minutes