Im a big fan of having lots of pinpoint removal spells, especially ones that are instant-speed since you never know when you might need to handle a problem permanent without necessarily sweeping the battlefield, and Generous Gift covers a lot of potential problems
There also arent any dual tap lands to help with the mana base
I think this is really strong as you can send out a card you no longer care about, (such as a land) or if you can recur it (such as said land when you control a Ramunap Excavator and you can just replay it)
Out of all of them, Doubling Season is going to be the most powerful, and, as you probably guessed, also the most expensive
This document was gifted to MORT (a stalwart of the storyline forums, who you may have seen commenting on this blog) after which it circulated on MTGSalvation and Phyrexia.com, before settling down on No Goblins Allowed, where you can read it in all its glory