Originally Posted by armonistan
You fail to answer the question in any meaningful way.
Believe it or not, I'm not trying to troll. I just find it hard to take this answer too seriously, so yes, I may sound a little ridiculous. But I'm trying to honestly answer your question. With humor attached to it of course.
If you want a completely serious answer well, here it is. It would feel just like being set on fire, the reason it would be different from champions such as Brand is because of the fact that it is true damage. Brand's magic isn't able to penetrate champion's innate magic resist, so they are able to "ignore" some of the pain, but the power of summoner's magic allows them to bypass magic resist and cause the complete and unresisted pain of being immolate by fire.
Which won't feel nice.