PF - Surreptitious Wizarding as a Mimic?

[unseenmage]

I have a character with a need to be able to cast spells whilst transformed.

This character has the powers of both a mimic and a doppelganger. The party is unaware of the character's true nature so even while in a humanoid form it will need to be able to cast spells and have no one know it was responsible.

Could folk please give me the rundown on spellcasting surreptitiously in PF?

[Hunter Noventa]

The most basic way to do that would be to use the Silent Spell and/or Still Spell metamagic feats. Unfortunately these do raise the spell level so it'll greatly limit your spell choice.

[Psyren]

Are Psychic Spells an option? You can cast those regardless of form, so that might be your best bet.

Either way, for sneaky spellcasting you'll need a feat (either Cunning Caster (https://www.d20pfsrd.com/feats/general-feats/cunning-caster/) or Conceal Spell (https://www.d20pfsrd.com/feats/general-feats/conceal-spell/) usually) to hide what you're doing. In Pathfinder, it's assumed that all spells, even those without verbal and somatic components, have some kind of dispaly that at the very least makes it possible for an onlooker to deduce magic is happening. The feats above help with that, and both are easier for psychic spellcasters to use.