Notes & Combos
Basic Harpie list. I opted for a tad more aggression than most, maxing out on all the low-leveled debuffers and 3 Seal. This lets the deck play its best around battle tricks, while the Seal and Harpie Middle do their best to keep the bodies in rotation to accomodate for the tech choice of the Alligator.
I went to Gold 5 with a more traditional list, using a combination of Light Angels, Music Princess Recital, and Trick Pigeons, but I found the Recitals were often dead, due to the prevelent backrow removal of the Cyberse deck. While I accepted by bad matchups against Maximums with the Traps, correct (more like, obvious) attack order just made Music Princess a liability and it was only ever good when I had Dragon + Sister on board.
I switched to Counter Pigeons for a bit, but I really didn't like how it was dead when I was on anything but the Harpies. Sure, the protection on Faith Bird was nice here and there, but I found myself pitching my birds to Thunder the Thunder often, allowing me to get Seal / Harpie shuffles ASAP, so my board would consist of non-Winged Beasts on the regular.
Hence the switch to an aggressive build. The theory is that, while the Seals are awful early game (and you will see them often with 3), the backrow you would draw into would be not as impactful anyway compared to other lists (oh, to be a 2500 ATK wall under the cushion of The Barrier). So, if I'm comparing the two, I would much rather max out on the card that is incredibly impactful in the middle and late game.
Think of it this way: Seal's participation early game is non-existant, Music Princess' is marginal (you can never open Sisters + Dragon + MPR), and Trick Pigeons is good with Sisters but bad as Seals without it. MP becomes a liability in the middle/late game and Trick Pigeons is still reliant on Sisters (and sometimes Faith/Harpie/Tyone, if the opponent is greedy), while Seal will always put in work, and overcome the Harpie deck's greatest weakness: 2500 ATKers with The Barrier. Being able to recycle your debuffers, which Harpie Middle can't, is a a boon too.
Anyway, a lot of words for what a simple, and I hope, intuitive conclusion to why I chose the techs I did.