Your board will fill with low-level Treats and Weapons. Do not feed them individually. Store them in a "merge chain" along the edges.
Before we dive into the specifics of Sibling Rivalry, let's cover some basics of Necromancy: sibling rivalry necromerger guide repack
Unlike the bee-focused NectarMerger, Sibling Rivalry is about balancing with Damage Output . Your board will fill with low-level Treats and Weapons
Would you like a for the first 24 hours of a repacked run? sibling rivalry necromerger guide repack
Why is the community so obsessed with "repacking" guides for this event? Because the rewards are too good to pass up on a "bad run."