"merge", "fusion" etc. tags

I’m a bit confused on how to tag original characters that are the product of merging the designs of existing ones.  
In particular, I uploaded >>2364634, which the artists states is a merged design of TreeHugger and Pinkie Pie.  
Some possible fitting tags I found are  
merge  
merging  
conjoined  
fused  
fusion  
combined  
we have become one
 
I assume the two main categories for this scenario should be  
a) characters actively merging as part of a story &  
b) an original character design as mentioned above  
but then fusion implies merged and we have become one implies fusion, which complicates it further.  
So it might be helpful to reduce all these tags down to two(?), like merge for designs and fusion for the action, and give them fitting explanations.

Well, just some quick opinions based on what I see already tagged each way:
 
merge - characters physically present and anywhere in the timeline of physically merging, from before it starts through completion  
merging - images specifically of characters in the process of physically merging  
conjoined - a state of being where characters bodies have been merged in a way that they have distinct, contiguous patches of their original bodies represented, eg. “siamese twins”/ multiple heads…Janus heads with half of each of two characters faces glued together…a whole unmodified set of wings stuck on another character…etc.
 
Also valid for characters designed from whole cloth as a conjoined character who never existed in a separated state.  
fused - almost synonymous with “conjoined” except only applying for characters which existed separately. Strangely, it does not seem related with “fusion” despite the linguistic relation.  
fusion - sometimes used for either merged or fused, but furthermore includes new/“remix” character designs not based on cutting-and-pasting pieces of other characters, but more conceptually integrating their designs into a whole new derivative design. May be done as a pure artistic exercise, or via magical means, or with the intention that the fusion design is the offspring from all parties involved.*  
^{*brand new sentences…}  
combined - I dunno what makes this different. I’d interpret it as “fused” seems to be interpreted now. With only 10 tagged images, it doesn’t seem to have a developed meaning.  
we have become one - any of the above, but with a certain additional “epic”, “evil”, or “unpleasant” quality. I think it’s over-applied.

@Background Pony #A2BA  
This is already really helpful. Perhaps it should be used to clarify the tags to make them more distinct.

We definitely have too many of these tags, even if there are definition differences. “We have become one” and “combined” will probably be the first targets to alias.

@Princess Luna  
That’s good to hear.