Fossil (October 10, 1999) The second expansion is the smallest standard set of the WotC era, with just 62 cards
Both of these things lead to far more non-creature cards being played in most archetypes
Market research showed that hybrid mana was the highest-rated thing in the original Ravnica block, and I believe it is still one of the highest-rated "mechanics" (it's a tool, not a mechanic, but that's what the market research called it), if not the highest, of all time
The Team Rocket Dark Charizard (1997) introduced the Dark-type variant and remains a fixture of vintage binders, while the Neo Destiny Shining Charizard (2001) is arguably the most desirable old-back Charizard of all the textured shiny foil treatment and estimated sub-1% pull rate from the original Japanese Neo Destiny packs make PSA 10 copies genuinely museum-tier
Yes, it helps out your opponents, but it helps you out far, far more