If I kill the Firemane with de pyroblast (Fire Wizard), I can´t take it as a trophy. But can I take a Riding Horse???

I think NO... But my friends say YES...

If you Pyroblast Firemane you kill it and may not take a Riding Horse.

To gain Firemane as a riding horse you have to defeat it in actual battle. Pyroblast is an out of sequence event before battle takes place and not part of the actual battle attack score.

Battle represents taming firemane for use as a follower. Pyroblast incinerates firemane killing her. Poor horsey.