Hello.
An hour ago I did some kind of ritual to release rage and the idea was to send it to the flame of a candle. I did and closed my eyes after a few minutes. Without purpose I experienced fire kasina. It was pretty cool and unexpected. I saw a strong red dot for maybe 15-30 seconds afterwards. Surprised of how long it lasted. It did not resemble the light I was looking at either.

That sparked a curiousity to experiment with fire kasinas. Seems like a fun practice.

Any ideas on how to creatively play with it?

I'm not sure what you mean by "creatively play," but if you take the red dot as the object of concentration and use that as the kasina, then it is possible you will eventually be entertained by a lovely light show of coloured nimittas ... and possibly more further down the track!

There are a few DhO threads on fire kasina that are worth exploring but sometimes it is best to just do the practice with an open mind and not read too far ahead (as it creates striving which can mess with concentration). 

Cheers
Anna

Lots of information on stuff to play around using the Fire Kasina on this website:

https://firekasina.org/

Read the fire kasina chapter in mctb 2nd edition as well. It is online if you dont have a hard copy.

"Playing with it" sounds like color control or form control. It usually takes a few days of continuous practice to gain that. However, maybe not. I would start off with setting the simplest intentions. For example, if you see a red dot, intend for it to spin or get bigger/smaller. If you see static, try to organize it. Whatever change is occurring in the visual field, try to increase it. Set the intention and patiently let it go.

It really doesn't matter what you do/see as long as you are fascinated by it. 

Spot on. I would just add that color/form control are not necessary for success in the FK. There are other options as well, for example Luminous Jhanas, Insight, exploring "dullness", Magick, and so on.

When you say "exploring dullness", are you talking about diving into hypnagogic imagery, or do you mean something else?

Asking because the imagery I see when drifitng into sleep seems more defined and stable since I started doing FK practice. Additionally, there was a weird FK sit where an image caused a trance-like state, but I was able to detach from it. It had a different feel from simply snapping out of a hypnagogic trance. Like being in the trance, but also having metacognitive awareness of it.