I am not here to rain on jpmeyer's parade. "I hate this place" is a great article. That said, here are a few things on "Rotations:"
In Standard, cards rotate out. That's it. Never play with them again. In Vintage, they don't. That's it. Play with them at your own peril.
jpmeyer's point about old sets being reduced to just a few cards is true. New cards come along, and make old cards comparatively less efficient. Whole decks are wiped out this way. But look at Bazaar. Squee (and some decks) made it a $100 card instead of a $20 card. Same for Mishra's Workshop.
These cards existed before deckbuilders figured out how to use them the way we all use them today; they existed before the designers printed new cards that pushed them over the edge. Can you play Workshop in Standard? How about Bazaar in Standard?
To come at this another way: Force of Will was good the day it was printed. If Force of Will was reprinted, it would still be good in Standard; then it would rotate out. Elvish Spirit Guide, however, is just now seeing resurgence in Vintage because it speeds up decks. It was always there, but new cards and more sophisticated deckbuilders made it playable.
I'll admit, no tournament Vintage deck is going to run Grizzly Bears over Wild Mongrel, but Magus of the Unseen "rotated" in; you never know.
's and "s fixed. Please don't paste straight from MS word.
-Jacob
