Base morph: Instead of consuming a corpse on cast, it will consume a corpse in the area once every X seconds to increase the damage and duration up to a maximum duration and damage increase
Avid boneyard: same as base morph but access to self synergy and possibly greater values for the damage and duration increases
Unnerving boneyard: still applies breach and vuln and instead of consuming corpses to deal increased damage instead generates a corpse every X seconds

These changes would better suit necromancer theme of more powerful the more corpses there are available while also differentiating the morphs more so to a corpse rich build such as blighted blast bones use or a corpse hungry build such as sacrificial blast bones or corpse burster builds