People still use Lord of D. huh? That card is so weak no one bothers.
Not even people using Disaster/Hopeless Dragon deck bothers with it, as far as I know.
I wonder why you have a problem with it, it only has 1200 ATK and no self protection.
And assuming you already gets rid of Lord of D. (that's easy) you can try Cybernetic Magician. Discard 1 card, change the ATK of opponent's Dragon Master Knight/Five-Headed Dragon to 2000, hit them with anything that has ATK higher than 2000 (including Cybernetic Magician itself, who has 2400 ATK), watch opponent goes mad
Not to mention Cybernetic Magician is LIGHT, it goes through Five-Headed Dragon's effect. Once FHD is destroyed, it's gone forever, because it can only be Special Summoned by a Fusion Summon, which means it cannot be revived via Monster Reborn or similar cards. Your opponent's only option is to fuse another one.
Now, when your opponent fuse another one, just use anti-summon cards, the most commonly used ones would be Solemn Warning and Solemn Judgement. Summoning is negated but the materials (including the fusion spell) still goes away, so your opponent used up all his resources for nothing.
This works best if your opponent is trying to summon Dragon Master Knight, as DMK requires another fusion (BEUD) for its material, assuming your opponent does not use a Fusion Substitute that is.