This is my optimized Harpie-Deck. I dont really have all the cards, but this is how it should look like. Quick explanation of card choices. Underdog is a real beast of a card in a deck where you have only normal monsters. It happens often, that it drew me 6 cards and led me to a win automatically, just because of the card advantage. It also guarantees you to draw a Spell Trap Card, may it be the initial draw or the fifth.
Curse Of royals protects your harpies field spell, or your mirror walls, or heart of the underdog.However, if they despell your HHG in their first turn, its not automatically a game lose, because of the other good beaters together with Order to charge and underdog, which is almost untouched, because they used their Twister/despell on HHG. And if they pull another, you most likely have already drawn a shit ton of cards or set curse of royals up.
You can swap out curse of royals for another good card like Metalmorph if you think you dont need it. Dunames can be switched out for Warrior Dai Grepher or for other 1700dmg beaters, but they should be non effect monster, because of order to charge. One OTC can be switched for Michizure. Michizure has the upsite of killing a second Monster, when you have it set and use order to charge in conjunction. The downside though, it is a reactive card and wont impact the Board immediately.
If you still need high attack beaters, take Skull Red Bird. But if HHG gets destroyed it is only a 1550 dmg monster. Jerry is a must have, it survives Ladybug of Doom and has the highest ATK without disadvantage. Keep in mind Dunames gets debuffed by Yami Field Spell! The Twister in there seems random, because harpies do the job better, however its your backup S/T Removal when HHG gets despelled or in general, when you want to kill another S/T card in the same turn you played a Harpie. Riryoku, Metalmorph, Reinforcement, Black Pendant are cards you can sub in for anything you might not have.