You can use Craft Illusion to anchor an illusion to a creature instead of an object, tailoring the illusion to allow your target to assume the appearance of another creature and shrouding them in an illusory disguise.
Make a Deception or Arcana check (whichever modifier is higher) to determine how well-crafted the disguise is. If you are applying the disguise to a creature other than yourself, or you have a mirror handy when you apply the disguise, you can see the result of the check and can choose to repeat the ritual to reapply the disguise if it is not satisfactory; if not, the GM should make the check in secret. Compare the result of your check to the Will or Perception DC (whichever is higher) of creatures observing you:
You only need to compare your result against a creature’s relevant DC once per application of the disguise. However, each time you are Hit or Critically Hit by an attack, you must reroll the Arcana or Deception check to make sure that your disguise doesn’t slip, the result of which is then compared to observers’ DCs as usual.
You do not have to Sustain the illusion to have it continue to match the target’s movements and facial expressions, but you can only affect a number of creatures equal to your Tier with this version of the ritual.
The creature you are attempting to impersonate must be similar in basic body shape and size to yourself (i.e. a Medium humanoid with two arms, two legs, and one head if you are a Human). You can attempt to assume the guise of a creature of different size or body plan, but doing so imposes a -4 Penalty to your Deception or Arcana check(s).
The maximum size of the disguise can be as large as the maximum size normally allowed by Craft Illusion, but remember that the illusion is intangible — if you disguise a human as a Giant, for example, they are still only able to manipulate things with their own (human-scale) hands, which can result in the odd sight of objects floating around in the illusory giant’s kneecaps if you’re not careful. The Kinetomancy ritual and Telekinetic Field spell can alleviate this to some extent, if used cleverly to manipulate objects at the same time the illusionary disguise is doing so.
Note that this ritual does not grant any acting ability or knowledge of the creature you are impersonating — you may look like them, but whether you behave like them is up to your Performance (Acting) and Deception skills.
You can expend 1x Tier 2 Occult Component to reduce the casting time of this ritual to 1 Minor Action.