モリガンは神話サイクルの文書にも登場する。12世紀の偽史編纂物『Lebor Gabála Érenn』(「アイルランド奪取の書」)では、トゥアハ・デ・ダナーンの中でエルンマスの娘の一人、ヌアダの孫娘として挙げられている<ref name="LGE-62,64"/>。
エルンマスの最初の3人の娘は、エリウ(Ériu)、バンバ(Banba)、フォドゥラ(Fódla)と呼ばれている。二人の名前は「アイルランド」の同義語で、それぞれアイルランドの最後の3人のトゥアハ・デ・ダナーンの王であるマック・グレイネ(Mac Gréine)、マック・クイル(Mac Cuill)、マック・ケシェト(Mac Cécht)と結婚していた。彼女達は土地と王権に関連しており、おそらく三重の君主の女神を表しているのだろう。次に、エルンマスの他の3人の娘が登場する。バドブ、マハ、そしてモリガンである。3人は裕福で、「狡猾の泉」、「激しい戦いの源」であると、歌詩で表現されている。モリグー(Morrígu)の名前はアナンド(Anand)とも言われている<ref name="LGE-62,64"/>。17世紀のジェフリー・キーティングの『アイルランド史』によれば、エリウ、バンバ、フォドラはそれぞれバドブ、マハ、モリガンを崇拝していた<ref>Geoffrey Keating, The History of Ireland |url=http://www.ucc.ie/celt/published/T100054/text021.html, Book 2 Section 11</ref>。
The first three daughters of Ernmas are given as [[Ériu]], [[Banba]], and [[Fódla]]. Their names are synonyms for "Ireland", and they were respectively married to [[Mac Gréine]], [[Mac Cuill]], and [[Mac Cecht|Mac Cécht]], the last three Tuatha Dé Danann kings of Ireland. Associated with the land and kingship, they probably represent a [[triple deity|triple goddess]] of sovereignty. Next come Ernmas' other three daughters: [[Badb]], [[Macha]], and the Morrígan. A quatrain describes the three as wealthy, "springs of craftiness", and "sources of bitter fighting". The Morrígu's name is also said to be Anand. According to [[Geoffrey Keating]]'s 17th-century ''History of Ireland'', Ériu, Banba, and Fódla worshipped Badb, Macha, and the Morrígan respectively.<ref>{{cite book |first=Geoffrey |last=Keating |title=The History of Ireland |url=http://www.ucc.ie/celt/published/T100054/text021.html |chapter=Book 2 Section 11}}</ref>
The Morrígan also appears in the ''[[Cath Maige Tuired]]'' ("''The Battle of Magh Tuireadh''").<ref>{{cite web |title=The Second Battle of Moytura |url=https://www.ucc.ie/celt/published/G300011/index.html |website=Corpus of Electronic Texts Edition}}</ref> On [[Samhain]], she keeps a tryst with the [[Dagda]] before the battle against the [[Fomorians]]. When he meets her, she is washing herself, standing with one foot on either side of the river Unius, near [[Riverstown|Riverstown, Co. Sligo]]. In some sources, she is believed to have created the river. After they have sex, the Morrígan promises to summon the magicians of Ireland to cast spells on behalf of the Tuatha Dé, and to destroy Indech, the Fomorian king, taking from him "the blood of his heart and the kidneys of his valour." Later, we are told, she would bring two handfuls of his blood and deposit them in the same river (however, we are also told later in the text that Indech was killed by [[Ogma]]).