The reserved list consists of 572 cards from Urza's Destiny and earlier that will never be officially reprinted by WotC
Others are niche, fragile, or even a little weird
Hydra also counters ping damage from Steel actions and characters, as whittling him down with Grab Your Sword or Smash will just cause your opponent to soak damage with their own characters too
This pair aren't normally going to be in the same deck, but they are both in the same genre of dork - making a Merfolk beater with big card flow attached for 6 or 7 mana
These are in Play and Collector Boosters, available in non-foil, traditional foil, and surge foil versions
Aetherdrift Aetherdrift play boosters is a tough one, because just like a race, there's only one winner and if you have 10 guilds racing like this set, nine losers