I noticed that we have mixed-design×63 tag that did not have any wiki excerpt. Many of the questions are about https://en.wikipedia.org/wiki/Mixed-design_analysis_of_variance, i.e. ANOVA analysis with between-subject and within-subject factors. But a noticeable fraction of the questions is about mixed models, or about something else entirely. And indeed the term "mixed design" refers to experimental design and so in a way is very broad, encompassing large fraction of the mixed model questions. I don't think this is a productive tag.
My suggestion is to go through all [mixed-design] Qs, remove the ones that are not about mixed ANOVA, then rename the tag into [mixed-anova], and then make it a synonym of anova. The idea is that in the end we have anova and mixed-model, and Qs about mixed ANOVA should go into [anova].
An additional complication is that we also have a split-plot×53 tag which is basically the same thing, but is more of a niche terminology. My inclination would be to leave it as is. Current wiki excerpt:
An experimental design used in situations where one factor can be changed more easily than another one. It's also called "mixed design" because it involves between-subject (hard to change) and within-subject (aka repeated measures; easy to change) factors.
PS. This is a continuation of Let us merge [mixed], [mixed-effect] and [mixed-model] tags.