use warnings;
use strict;

while (<DATA>) {
    chomp;
    next if ! /^(\d+) (?:MatchMe \[|I need to be dispatched.*\:\s)(.*?)\]?$/;

    print "Line $1, reason: $2\n";
}
__DATA__
111 MatchMe [This is why]
222 I need to be dispatched to the same callback: For This Reason

##</code><code>##

Line 111, reason: This is why
Line 222, reason: For This Reason