Do Errant and Giada and Rattlechains allow me to cast Spirits without flying or flash from my library?

Question

Very similar to the related question: Do Errant and Giada and Rattlechains allow me to cast Spirits with flying from my library at instant speed? That question deals with Spirits with flying, while this question deals with spirits without flying.

Errant and Giada allows you to cast spells with flash from the top of your library.
Rattlechains allows you to cast spirits as though they had flash.

Does a spirit benefitting from Rattlechains' ability cause it to also benefit from Errant and Giada's ability, and allow it to be cast from the library even though it did not have flash or flying naturally?

Answer 1

No, this combination of cards will not allow you to cast Spirits without flying or flash from the top of your library.

Rule 609.4 says

Some effects state that a player may do something “as though” some condition were true or a creature can do something “as though” some condition were true. This applies only to the stated effect. For purposes of that effect, treat the game exactly as if the stated condition were true. For all other purposes, treat the game normally.

Rattlechains ability "You may cast Spirit spells as though they had flash" applies only to determining when you can cast Spirit spells. It does not extend to evaluating the condition on Errant and Giada's ability.

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In contrast, if you controlled Teferi, Mage of Zhalfir, along with Errant and Giada, you would be able to cast any creature spell from the top of your library.