Okay let me try my best.
First, any altcoin that wants or demand you share your private keys, mnemonic phrases is fake. As the nature goes, it is meant to be private, even when creating the wallet, you were warned about sharing private informations with a third-party, hence any airdrop asking for it, is fake.
Secondly, any airdrop asking for payment of any kind is fake. Airdrops are carried out to help promote a project and when done, the project team in return rewards the participants, therefore any airdrop now asking for payment means they are fake and looking for who to scam.
Thirdly, any airdrop whose social media accounts like twitter was created recently most times barely a month prior to the launching of the project is likely to be scam. There are many of them on telegram and twitter.
Fourthly, most airdrops from most projects have no idea on whatever they want to build, just create a telegram group, twitter and promotion starts, and within a few days they start talking about Pre-sale. I do not think projects like this are serious. Also, with DeFi still very much around, many of these projects are coming up with full force hence be careful.