Card Rulings:Brotherhood of the Fire Fist - Horse Prince

OCG Rulings

 * Even if "Skill Drain" is activated after "Flaming Star Marquis - Hoshin" is Synchro Summoned, the effect that prevents you from Special Summoning other level 5 or higher monsters is not negated. Therefore, you can't Special Summon level 5 or higher monsters. Also, if "Skill Drain" is already active and "Flaming Star Marquis - Hoshin" is Synchro Summoned, afterwards, you can Special Summon level 5 or higher monsters.