Teifling Alter Form Questions

[Deaxsa]

that grants me a fly speed and allows for usage of full spellcasting (granted, i have eschew materials) (so far i've only seen mephit, imp, and quasit which allow flight and spellcasting)

or can i cast spells (even those with somatic components) as an Arrowhawk/Tojanida/Xorn?

can i burrow if i alter form into a Xorn?

if i alter form into a Ravid, which has supernatural flight, can i fly or not? it does not even have a landspeed. would i just flop around on the ground? that's the arrowhawk i'm thinking about

also, can i disguise my casting of alter form so it looks like i am casting polymorph? (with sleight of hand or something)

NB: trying to stay in core. other answers are not necessarily bad, just that they will need DM approval.

[The Viscount]

You could potentially cast as a xorn or less humanoid being, but if it is too nonhumanoid or not capable of speech, you would need surrogate spellcasting. You would gain xorn's burrow. You could not fly with anything that flies supernaturally. You may disguise alter self as something else through the False Theurgy skill trick, or conceal it entirely with the Conceal Spellcasting skill trick.