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, Retreat to Coralhelm and each Scute Swarm you control triggers.
Resolve each Scute Swarm trigger, creating that many 1/1 Insect creature tokens or that many token copies of Scute Swarm.
Resolve the Retreat to Coralhelm trigger, untapping Wight of the Reliquary.
Repeat.
Results
Near-infinite ETB.
Near-infinite landfall triggers.
Near-infinite creature tokens.
Put all land cards from your library onto the battlefield tapped.