[Varyon]

Treat some of the Striga's HP/ST as Massless +0% - it doesn't contribute to resisting knockback, but it also doesn't increase the damage the creature/character takes from falling or being flung into walls. That markedly reduces the damage necessary for knockback. If the Striga only has HP 10 for purposes of calculating the knockback threshold, knocking it back 6 yards (which is pretty impressive) would "only" call for 48 knockback damage - 7d cr dkb will pull that off reliably, but better may be to designate some of the damage as knockback-only (which would be No Wounding, No Blunt Trauma, and Double Knockback). So, say, 2d cr (Double Knockback +10%) [11] + 6d cr (Double Knockback +10%; No Blunt Trauma -10%; No Wounding -50%) [15] (away from books, so you'll want to check those numbers) could be treated as 2d cr with 8x knockback. RAW, I think you might have to add Link +10% to each, but I wouldn't require that.