SYSTEM Tablespace is Growing Abnormally in 12c

My SYSTEM tablespace was growing rapidly. This was happening in my test environment. We observe that we 

Database version is 12cR1

1)    Some has assigned default tablespace as SYSTEM
2)    Auditing is ON and consuming more space.
3)    SYS_LOB Objects uses lot of disk space
4)    Data dictionary objects uses lot of disk space

So now, how to find the root cause and what could be the solution?

Let’s query to dba_segments table to find the root cause. I came across few scenarios in my different databases. 

Use below query to find out what are those segments which are consuming lot of space in SYSTEM tablespace.
select owner,segment_name,segment_type
 ,bytes/(1024*1024) size_mb
 from dba_segments
 where tablespace_name = ‘SYSTEM’
 order by size_mb desc

Scenario 1

Problem
Auditing is enabled hence AUD$ table is growing very fast. Organization wants to do auditing and there is 

Visit https://support.oracle.com  there are many notes available for this issue..

Scenario 2
Check below screenshot,

You cannot move those tables to another table space or truncate or reorg of these table. Oracle strictly says that 

Answer is, Yes, this is the ideal scenario and we don’t have control over it.

Scenario 3
SYSTEM tablespace growing unexpectedly after database upgrade OR after IMPDP

If you are upgrading your database from 11g to 12c, this might happen that you observer some unexpected 

Here I would like to highlight that when you do the data import; import do lots of compilation of your function, 

Here the workaround is to recompile the objects. This will decrease the logical space, not the physical space.
Run this command after impdp,
Example
1) alter session set events =’10946 trace name context forever, level 8454144′; 
2) exec utl_recomp.recomp_parallel(‘4′,’SCOTT’);   

Scenario 4

Many a times it has been observed that data dictionary tables are occupying more space like BOOTSTRAP$,