6 of 7 typo, grammar

Almost all shapechangers leave type unchanged. Metallic dragons, though, do change their type.

"Statistic," as a defined term, is spelled out on MM pp.6-11. The second element spelled out is "Type," of which both Celestial/Giant and Humanoid are instances. So which stays?

The Coautl's and Deva's shapechange abilities specify that they retain their statistics except for a few callouts which do not include type. Since their Celestial type is a statistic they retain it and are still Celestial while in humanoid form.

The Oni's shapechange ability specifies that the only statistic to change is size. Since type does not change, the Oni is still Giant while in humanoid form.

For completeness, the Quasit, Yochlol, Imp, Doppelganger, various weres, Mimic, Slaadi, Incubus/Succubus, Vampire, and various Yuan-ti are the other shapechangers in the MM. The Night Hag and Lizardfolk Shaman also change shape (ability) without being shapechangers (tag). All shapechange with similar verbiage to one of the samples above and so all retain their type.

Metallic Dragons' Change Shape ability does change type, as spelled out in their ability description.