i had 2 scarr , sangan and DAD in my hand i used Morphing jar and had five cards (sillva , monster rencrination and other cards) i used monster rencrination discarded sillva (its special summoned) and brought DAD. i had 3 dark mons in my grave so i summoned DAD.
this combo is easy to happen and i won a duel with that.

discarding for Monster Reincarnation is a cost and therefore does not activate the effects of Dark World monsters. Your combo does not work. Furthermore, this is not a combo because you got certain cards by random chance from Morphing Jar.

As Neko said....

These effects only activate if the cards are discarded by a card effect. They will not activate if discarded for the cost of a card like "Lightning Vortex", "Raigeki Break", "Tribe-Infecting Virus", or "Infernal Incinerator". They will not activate if sent to the Graveyard by a card effect like "Last Turn" or "Chaos Emperor Dragon - Envoy of the End".[2]


Also, so no confusion happens.
These effects can activate in the Damage Step, if discarded by the effect of a card like "Don Zaloog".[2]