mortars run this way faster than wisps for some reason, like way way faster, wisps are unbearably slow its kinda crazy, not upgrading still works but its like 25-30 seconds slower on avg(if you dont upgrade use a summoner with 2 huntress guardians on top of the pylon until the last round) if you dont have enough range on your guardian it might be a lot slower because the owls need to be able to target the wyverns while they are flying across (pylon makes it a lot more forgiving) 

i put my huntress set on my hermit to make the nature pylon range bigger so its easier to buff up both owl stacks but i was still doing it with about 4k range on him, its just easier with more range. On the 10th wave you need to bring in 2 tanky sword users to sit where the hint 5's are, the sword users will have 2 huntress guardians to speed up the mortars(make sure they are close enough to buff them but its only like 7-10 seconds slower if you dont buff them)

the buff beams dont need to be longer than 4 du, but in the video i make them longer just because it builds faster, the build has extra du open so you can just kind of spawn them fast without worrying about precision.

i realized after testing a lot with this build that if you wanted to run 2 summoners instead of the squires the bosses would just walk up top and it would be kinda cooked, you could probably solve this by putting ogres down below on one of the future waves but i dont think it would even really be that much faster and getting a bunch of swords is nice

video here for setup and what i mean for the boss(i set up 2 mortars behind in the video on accident but either way works)

https://www.youtube.com/watch?v=RtzkOo-HenU

https://imgur.com/a/ykAywlk