Modal spells had been part of the rules for a long time (it wasn't defined yet in Alpha ), but it wasn't until Khans of Tarkir that it was templated in such a way that it was clear in looking at a card what was and wasn't a modal spell (not that many players knew specifically what to look for)
Eat to Extinction Eat to Extinction is a great creature and planeswalker removal card
Which card earned this superlative
Megara Pulling the Strings is handy at turning Bobby or Sergeant Tibbs Courageous Cat into real threats
Example: Leyline of the Void is an enchantment that reads, in part, If a card would be put into an opponents graveyard from anywhere, exile it instead." Wheel of Sun and Moon is an Aura with enchant player and the ability If a card would be put into enchanted players graveyard from anywhere, instead that card is revealed and put on the bottom of its owners library." If the controller of Chittering Host is affected by both cards effects, that player chooses one effect to apply to the event and Midnight Scavengers and Graf Rats are both moved to the appropriate zone
If that spirit then leaves the battlefield, the original card goes to your graveyard