In Mk 12:31 the byzantine editions (Robinson-Pierpont, Pickering,BGNT 2014) all read:
Καὶ δευτέρα ὁμοία αὕτη , Ἀγαπήσεις τὸν πλησίον σου ὡς σεαυτόν . Μείζων τούτων ἄλλη ἐντολὴ οὐκ ἔστι
They take αυτη as a nominative, like it is in the critical texts, that have δευτερα αυτη in stead of και δευτερα ομοια αυτη.
Hodges-Farstad 1984 have αυτῃ, dative, fitting to ομοιος that has dative according to Montanari.
In the INTF mss there are some mss with explicit dative (αυτηι : 1, 26, 124, 154, 543, 569, 700, 826 (first hand) and 1582), two have ταυτηι (826 corrector; 788).
The versional support of dative is quite large: Tatian (§34,30), Peshitta (translation Lamsa), Old Latin, Vulgate Jerome, Gothic, Armenian, Aethiopian.
Most old critical editions (Griesbach 1777,1796), Scholz (1830), Tregelles 1879 (he has αυτῃ in his text), Tischendorf have the dative-variant in0 their apparatus. As Von Soden, NA - all editions - and ECM don‘t use diacritics in their apparatus, their position is not clear. The other 19th century critical editions don‘t mention here the dative (Baljon, Merk, Vogels, Bover, Souther)
What would be the most plausible case: nominative or dative? And if nominative, how is ομοια to be understood?