I'm using Ignite 2018.1 with the included MVC5 helper dll (Assembly Infragistics.Web.Mvc, Version=5.18.1.40, Culture=neutral, PublicKeyToken=7dd5c3163f2cd0cb)

This Razor code:

@(Html.DefaultComboUnbound("ddlAllChangeTypes", "AllChangeTypes", "Key", "Value", Model.ChangeTypeDescriptions.ToList(), null)
    .PlaceHolder("Select to apply to all")
    .AddOrAppendClientEvent(ComboClientEvents.SelectionChanged, Html.IgEventHandler("ddlAllChangeTypesSelectionChanged"))
    .DataBind()
    .Render()
 )

Renders to this javascript function:

$(function() {
    $('#ddlAllChangeTypes').igCombo({
        filterExprUrlKey: 'filter',
        compactData: true,
        placeHolder: 'Select to apply to all',
        enableClearButton: false,
        allowCustomValue: false,
        dropDownOnFocus: true,
        width: '100%',
        valueKey: 'Key',
        textKey: 'Value',
        inputName: 'AllChangeTypes',
        loadOnDemandSettings: {
            enabled: false
        },
        dataSource: [{
            "Key": 0,
            "Value": "Soft change"
        }, {
            "Key": 1,
            "Value": "Hard change"
        }],
        selectionChanged: function(evt, ui) {
            ts1599461760.ddlAllChangeTypesSelectionChanged(evt, ui)
        }
    });
});

As noted in the documentation for igCombo the placeholder setting it generated is incorrect and does not work anymore.
https://www.igniteui.com/help/api/2018.1/ui.igcombo