When you Summon a monster, you can activate any Ignition Effect using your Ignition Priority. This means that you can Summon this card by discarding "Destiny HERO – Malicious", then activate that Malicious' effect in your GY immediately, before "D.D. Crow" can be chained to it.
Discarding 1 Level 5 or higher DARK monster to Special Summon "Dark Grepher" is a cost.
Discarding 1 DARK monster for the second effect of "Dark Grepher" is a cost.