Black Ragna is much more stable than red, since he is pretty much immune to early security checks (due to vast amounts of black blockers) and has the ability to de-digivolve your digimons (which includes your blockers) allowing other attacks to easily go through. To make matters worse, if [BT3-075] Craniamon has also been fielded then both red and violet removal cards will not be able to land on him (hence putting you in a unsurmountable handicap if you are playing either of those colors).
Therefore against black Ragna, it becomes imperative to destroy their digimon before they become Ragnaloardmon. A good moment would be Raijiludomon or Tialudomon, depending on your removal options. Ragnaloardmon is significantly less threatening without the proper inheritance effects from the ludomon line.