Migrating a tablespace to a different database on the same ASM How might one go about copying or moving tablespaces between databases that uses the same ASM instances? 

Might it be possible to cut some corners in RMAN or have ASM remap files belonging to a transportable tablespace?
Transportable tablespaces and asmcmd cp command should do the trick.


Prepare transportable tablespaces metadata set.
Copy expdp file to location accessible by impdp from destination database.
asmcmd cp datafiles to new location.
Import TT metadata set.


If your ASM diskgroup uses some storage device with several disks then you should be able to improve performance by copying several datafiles in parallel.