This card is treated as a Normal Monster while face-up on the field. While equipped with a "Noble Arms" Equip Spell Card, this card becomes an Effect Monster with this effect.● This card becomes DARK and its Level is increased by 1. Once per turn, if you control no other monsters: You can Special Summon 1 "Noble Knight" monster from your Deck in Defense Position, except "Noble Knight Medraut", and if you do, destroy 1 Equip Spell Card you control.
Effect can only be activated when equipped with a Noble Arms card and you control no other monsters
Here are the monsters you can special summon with the Effect of Noble Knight Medraut. You can then equip to them the Noble Arms card you destroyed with Medraut's effect. After Special summoning Ignoble Knight Black Laundsallyn, you can use his effect to tribute Medraut and search a Noble Arms card from your deck. You can special summon Noble Knight Borz and equip him with the destroyed Noble Arms card to search your deck for another Noble Arms card. You can also special summon Noble Night Drystan and equip him with the destroyed Noble Arms card for both protection and destroying opponent's cards.
Gee, maybe because Parallel Twister doesn't destroy your card, and is such useless for such a purpose? (Well, technically you CAN destroy your own card with Parallel Twister, but going -3 seems like a dumb idea.)