Wight of the Reliquary does not have summoning sickness.
You control at least one additional creature.
Steps
Activate
Wight of the Reliquary by tapping it and sacrificing another creature, causing you to search your library for a land card and put it onto the battlefield tapped.
When the land enters the battlefield,
Zendikar's Roil and
Retreat to Coralhelm trigger.
Resolve the
Zendikar's Roil trigger, creating a 2/2 Elemental creature token.
Resolve the
Retreat to Coralhelm trigger, untapping
Wight of the Reliquary.
Repeat.
Results
Near-infinite landfall triggers.
Put all land cards from your library onto the battlefield tapped.