Strength D does ignore invulnerables as I recall. Every army has answers for a knight. Marines have TH SS termies and assult marines with Melta Bombs, gaurd have suicide melta vet units, Chaos Marines, 2 Melta Guns in one squad, Deamons im not familiar enough with, Tyranids have all sorts of nasty claw upgrades, Necrons can glance it to death or use a C'Tan, Orks have nobs with powa clawz and I think they to have Melta Bombs, Sisters Heart Melta Weapons, Tau..offensive amount of Rail Fire and Marker Light spam, Eldar have bright Lances and Wraith Knights, Dark Eldar have Dark Lances and Hay wire Grenade Wytches, Grey Knightd have the babby walker and also TH SS termies. I think I covered every one Im not counting all the other marine codecies. Point is every army has an answer to a Knight one way or another.
Ide like to know who can ally with the knights?