Is it possible to only use an Oculus Rift (and skip the Google Cardboard requirement)?

Yes it is.

We teach you to set up the Oculus Rift before we come across any Cardboard specific content. The only section that relies on Google Cardboard is "Squashy Toad" so you can use your knowledge of the Rift to use that instead and skip the Cardboard specific lectures.

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