DG: Ahh, I wasn't aware that Spirits of Fire are immune to the cage trap trick. Good catch.
If you don't make it evaporate all water before it becomes immersed (like a Spirit of Fire does), then it's vulnerable to being encased in obsidian. Thus, swimming is irrelevant.
Unless you want to have it swimming in magma. Some other tags you might want to add are: [FIREIMMUNE][CANOPENDOORS][DRAGONFIREBREATH][FIREBREATH][FIREIMMUNE_SUPER][CAN_LEARN][EXTRAVISION][MAGMA_VISION][NO***][PARALYZEIMMUNE][SPEED:***][THICKWEB][WEBBER][WEBIMMUNE][AMBBUSHPREDATOR]
That's about it, I guess. In order, they allow your creature to: walk through fire; open doors; breathe fire; breathe fire in a cone; walk through it's conical fire; learn (gain skills and attributes); see without eyes, see in the dark...; see in magma; not need to sleep, thoughts, eat, drink, breathe and cannot be exerted, in pain, have emotions (but also cannot become enraged), have fear, be nauseous, have weapons stuck in it or be stunned; be immune to paralysis; be very fast (note: the lower your value, the higher it's in-game speed); have web that can catch large creatures; actually produce such web and be hidden until discovered.
You can also add a blood-sucking and paralysing attacks, increase damblock and size to ridiculously high levels, have it have ridiculously high attack values, add extra arms/legs/paws/... to make it able to grab and hold multiple enemies at once etc.
For further information I direct you to
the wiki page on creature tokens.