This is a theory, I realize there are many other possibilities. and the the writers will likely just change things to keep us hanging instead of developing a quality story.

RJ
has a strong connection to Visualize.  How many people play/mess/draw
with blood like Stiles did in his ceremony.  RJ obviously, makes his
smiley face with blood.  But I think when applied to the face is some
sort of forgiveness or mercy or pardon, like RJ did to Lisbon and like
Stiles did in the ceremony.  Stiles has some connection to RJ per his
previous conversations.  He is not RJ because ,,, well its just to
obvious.  But he has an interest in RJ's well being.  It makes Stiles
sad that RJ has become tied up in tiger tiger because he knows its not
consistent with Visualizes morals or RJ's future in visualize.  So he
helped RJ fake his death.  The reason Lisbon got to see Partridge dead
is so she could personally verify his death.  So partridge is laying on
the ground. Stiles grabs Lisbon, does his blood on face thing.   Swaps
Partridges alive body, probably with a very deformed face substitute dead body. 
And cuts off a patch of skin on the arm. because... RJ told PJ tiger
tiger earlier... so they assume PJ knows about the blake assocation by
now and either doesn't want Partridge linked to tiger tiger or doesn't
want to expose tiger tiger.  Now Partridge is assumed dead and can be
free from tiger tiger and free to lead Visualize because Stiles is
dying.  Now that Stiles is dead, Partridge wants to talk to PJ because
he lost a major helper and with losing his purpose for being, due to
betram's false accusation stealing his thunder, RJ is not thinking
logically and reaches out to PJ.