Does it Lead or Follow?
14. X86 Assembly (gcc 6.3), 324 bytes

.TITLE "a"#"a" ELTIT.
.data
i:.fill 25,1,0
s:.string "%25[^\n]"
t:.string "-&gt;Hi, Retina!"
f:.string "Bye Retina!"
.global main
main:           
pushl $i
pushl $s
call scanf
addl $8, %esp
pushl $i
call strlen
addl $4, %esp
sub $21, %eax
jz y
pushl $f
call printf
addl $4, %esp
jmp en
y:
pushl $t
call printf
addl $4, %esp
en:
ret


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Note: this will return a runtime error because the exit code is not zero. Running this in the ideone editor will display all stdout output regardless of how the program concludes.


Truthy output: "-&gt;Hi, Retina!"
Falsy output: "Bye Retina!" 


Satisfies:


The first character is a ..
It contains an e.
Its length is even.
Its length is a perfect square.
It contains an a.
It contains a &gt; character.
Contains the exact string -&gt;.
Contains the exact string Hi, Retina!.
The sum of the first two Unicode code points is a multiple of 5.
The 10-th character is a ".
The last non-empty line does not have any duplicate characters.
The first line is a palindrome of length > 5.
The first line is exactly 21 characters long (not including newline).


For future answers:


The first character is a ..
Its length is an even perfect square.
Contains the exact sequence -&gt;.
Contains the exact string Hi, Retina!.
The second character's Unicode code point, mod 5, is 4.
The 10-th character is a ".
The last non-empty line does not have any duplicate characters.
The first line is a palindrome of length = 21