mtg cards with lifelink Spirit Link (9ED-47☆) - Ninth Edition Foil Lifelink in MTG - Rules,

You could put it in a fat pack box, tape that up with another packing slip or copy of the shipping label attached, then put that inside a small reused amazon/ebay box with some reused packing material (you probably have some lying around)

It's worth noting that, just because a card has the Companion ability, doesn't mean it can't be played as a regular creature in your deck, or indeed as your commander

Ending the turn after the spell keeps pesky dies triggers from happening and hitting artifacts in addition to creatures is a clean answer for Cori-Steel Cutter

Airbender Ascension offers a cheap way to Airbend any creature in play, which is great by itself

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