In a deck with cheaper interaction and other spells, well, not so much
The quote below is modified with some additions/changes that were discovered later on: 1st Edition Timeline: Lets Iron it Out English: 1st Edition Prints Start: Base Set 1st Edition Prints End: Neo Destiny (Last w/ 1st Stamp) Sets Omitted: Base Set 2 Japanese: 1st Edition Prints Start: VS Series 1st Edition Prints End: Evolutions (Last w/ 1st Stamp) Sets Omitted: Entry Pack '08 DX (DP) - Raichu Deck only Lost Link Master Kit BREAK Starter Pack [XY Generations excluding Radiant Collection in English] CP4 False 1st Edition Sets (Sets with ONLY a 1st Edition Print): VS
Beyond that it's mostly generic upgrades like Smothering Tithe, Teferi's Protection, better land upgrades, better removal, the usual
While I personally find it fun to run pet cards and lesser played gems, its safe to say that there are a good number of strong Magic cards I wouldnt want to leave home without
Or one card and a 4/4 thopter
The creature that enters the battlefield doesn't need to have lesser power than Shadowfax (this can happen if it enters with +1/+1 counters on it, for example)