The Lesser Demon Champion attacks with both magic and melee. It uses very powerful spells which can hit upwards of 200 life points, and its melee attacks hit up to 150. The Champion uses only magic from a distance, and will use both melee and magic up close.
During the fight players cannot wear any armour or weapons. Therefore it is almost impossible to sustain the melee damage of the Lesser Demon Champion. The best way to kill him is by Magic, because runes do not count as weapons or armour, and the champion, being a demon, is extremely vulnerable to these types of attacks. This has been made much easier, as it is possible to autocast without a staff of any kind now. He is not immune to the effects of the poison caused by Smoke spells, so they can be used against the Champion as well.
Since the Lesser Demon Champion cannot detect protection prayers, it is advised to stand back and use the Protect from magic prayer against him. He will not use his melee attacks if the player is not next to him, and will only focus on attacking the player with magic. With the protection prayer on, his magic attack will almost never do any damage, so bring enough Prayer potions (1-2, depending on the player's Prayer level) to keep the prayer on and enough runes so that they don't run out mid-fight. It is wise to prepare for over 250 spells when going for a sure kill.
Remember to not let the prayer wear off, as the Lesser Demon Champion is capable of finishing off an unprotected player with even 99 Constitution very quickly.
The fire spell animation of the lesser demon champion has yet to be updated.