Dyadic ⍳ and other set functions (∊, ∩, ∪, and ~) are significantly faster for certain arguments.
The matrix iota idiom M{(↓⍺)⍳↓⍵}M which used only to operate on character matrices, now operates on any matrices.
There is a new idiom Catenate To (,←).
The atomic vector index idiom ⎕AV⍳CA is is not implemented in Unicode Edition, and should be replaced in both Editions by ⎕UCS.