I see this as having been merged; undoing one side of a merge forks content in large blocks. See here and here where the article was merged. The prior merge notice indicated discussion, scant, at Talk:Creature type (Dungeons & Dragons) which I see you commented at.
 Yes, I feel that most of the leaf-nodes are utterly non-notable; this is what lists are for (and those lists should largely consist of  unlinked critters). The D&D; 'verse has a near-endless number of named denizens and linking every one of them to a stub is absurd.
 The Aberration (Dungeons & Dragons) page has not been deleted; rather than simply undoing the merge, you are free to review the old versions of the page in order to mine them for bits you wish to add to the Creature type (Dungeons & Dragons) page. It would be nice if you cited sources establishing notability for anything you wish to resurrect. Cheers,