I made one to ban assign/2. then is next

defmodule GelaSkins.Credo.NoCallsToAssign2 do
  @moduledoc """
  Checks that `Phoenix.LiveView.assign/2` can't be called.
  """

  # you can configure the basics of your check via the `use Credo.Check` call
  use Credo.Check,
    base_priority: :high,
    category: :custom,
    exit_status: 0,
    explanations: [
      check: """
      Always use `assign/3` in favour of `assign/2`.

      This forces a pipeline when using multiple assigns.  The advantage here is
      that assigns may be added, removed, and re-ordered easily (no commas to deal
      with) making diffs nicer.  It also means you must explicitly name the
      parameters accepted by LiveComponents.  You cannot simply do
      `assign(socket, assigns)`.
      """
    ]

  @doc false
  @impl true
  def run(%SourceFile{} = source_file, params \\ []) do
    # IssueMeta helps us pass down both the source_file and params of a check
    # run to the lower levels where issues are created, formatted and returned
    issue_meta = IssueMeta.for(source_file, params)

    # Finally, we can run our custom made analysis.
    # In this example, we look for lines in source code matching our regex:
    Credo.Code.prewalk(source_file, &traverse(&1, &2, [], issue_meta))
  end

  defp traverse({:|>, _, [{:socket, _, _}, {:assign, meta, [_]}]} = ast, issues, [], issue_meta) do
    {ast, issues ++ [issue_for(:assign, meta[:line], issue_meta)]}
  end

  defp traverse({:assign, meta, [{:socket, _, _}, [_]]} = ast, issues, [], issue_meta) do
    {ast, issues ++ [issue_for(:assign, meta[:line], issue_meta)]}
  end

  defp traverse(ast, issues, _, _issue_meta) do
    {ast, issues}
  end

  defp issue_for(trigger, line_no, issue_meta) do
    format_issue(
      issue_meta,
      message: "Only use assign/3",
      line_no: line_no,
      trigger: trigger
    )
  end
end

It also checks for a single pipe into assign. I can’t remember why I did this instead of using the existing credo rule but I assume it’s because sometimes I’m ok with single pipes. This was a while ago.