What an eerie effect actually does on triggering will depend on the card
Decks that were already strong could now beat you in a whole range of new ways without ever having to tap out for more than a three mana-creature, and once that creature was on the table it felt like it both dramatically slowed your ability to attack and made the situation worse on a continual basis as every turn that went by meant another card (or often cards) available to the opponent to make Dr
The best payoffs are ones that put counters on themselves (like Tellah, Great Sage and The Emperor of Palamecia) for casting expensive noncreature spells to make them bigger combat threats
The mechanic itself is pretty powerful on some cards, and luckily, most of those reside in the red and green mana pools
All the Swamps from Beta were done by Dan Frazier, who hasn't done a ton of work in Magic's later years but did provide art for various Signets, Talisman, and Moxen for Secret Lair and Mystery Booster 2
She hesitated during their confrontation, but lost control in a fit of rage when she realized the senior baron was experimenting on her deceased mother