At the end of the 2 hour series Permiere we saw that Boone and the Red Devil killer are most likely working together to take out the sisters of the KKT house.
My theory is 'what if Boone is the baby from the 1995 party and what if Gigi was the one sister trying to help the babys mother.' Gigi said herself that she experienced a tragic even in the 1990's and that she was a past sister of KKT. She could have taken the baby (Boone) and raised it as her own.
They would both have reasons to want to kill the girls of KKT. Gigi wants to redeem herself for letting her 'sister' die. Boone would want revenge for his mothers death.
Gigi could be the non-murdering Red Devil (Knocking out Pete/Stalking Grace) and she could be helping the Red Devil killer (Boone) get into the house by leaving windows/doors open and distracting poor single fathers trying to protect their little girls. This also explains why the Red Devil killer didn't want Pete seeing who was in KKT in 1995. It could give away Gigi's name or if she was related to anyone in the house.
Boone could be the murderous/hilarious Red Devil killer that is running people over with lawn mowers. He clearly doesn't care about hurting other people since he and Chad are first seen hitting innocent people with golf balls. It could also explain why Boone was 'killed' off so early. This would give him free range of the school since no one would be looking for a dead student and this way Gigi could always be around the girls to give herself an all alibi.