not all airdrops need gas, I have participated in several airdrops where I only needed my mail, for example: Blockchain had an airdrop where you could claim stellar, the Coindeal exchange had an airdrop in which it launched its own currency and I could withdraw without problem (I think it still works) and finally Yoda from the Yobit exchange also had an airdrop that combined 2% of what the airdrop paid you, the good thing is that it could be withdrawn daily.



I think that what you are referring to is the hybrid projects between ICOs and airdrops, they basically give investors privileges, but I think they are very dangerous, they can scam us.