To kill thr shieldspire just walk into it(just walking around near him), wait it let his shield down then HIT X 1 time. Do it 3 time and you get red key.
To complete today challenge, put a Monkey Village (2/3) or (1/3) on the second planet. Put bomb tower (4/2) on right side of first planet or top left of second planet set it target to first. put Supermonkey (2/1) on the middle of second planet then upgrade to (3/1) as fast as possible. wave 60 set super money target to STRONG and try to put another bomb tower at bottom right of second planet then upgrade it to (4/2). after that put another super monkey upgrade it to (3/1) or (3/2) set target to FIRST. Try to upgrade super monkey to sun god (both of them) and win the challenge.
I have special building (super monkey lv2) and have 46 life left at the end, no special agent used.
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 "Loot Hero"){kind=icon}
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 "Obliterate Everything 2"){kind=icon}
 "Seedling"){kind=icon}
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That may be possible. In the mean time might I recommend using the tag search for "Small, Medium, Large"