Infravision, which I never really liked. I was OK with it when people just assumed that it was like normal vision, only in the dark; but then Predator came out and ruined it for everyone. I like the 3e way of splitting it into low-light vision and dark-vision better, but they still both kind of suck. They only exist so all these dungeon dwelling creatures won't need a light source and to give people an advantage to playing a non-human race. I see the logic to the first point, but not really the second; I mean if EGG really wanted lots of people playing demi-humans why the level limits? And why do Halflings get infravision? They are, for all intents and purposes, just tiny humans. Often chubby and with hairy feet, but pretty much human other than that. Why do Elves need infravision? They live above ground too. I can kind of understand the Dwarves and Gnomes because of their preference for deep subterranean living. But Elves live in the sunlit forests.
I is for Initiative. Why is initiative reworked for every version of the game? Why is it still inadequate regardless? The best initiative system I have ever seen was one my 2nd edition era Oswego group invented with phased movement based on your rolled individual initiative (with dexterity modifier), movement speed (size, strength and armor type were considerations here) and weapon speed. It was needlessly complex and still didn't manage to adequately solve the problem of reach weapons, but we all understood it at the time and it kept everyone focused on combat because everyone was pretty much always moving. If I could remember exactly how that system worked I would probably add 3e attacks of opportunity and call it perfect.
I is for Imbolc on of the four major festivals of the Celtic year. Traditionally celebrated in the beginning of February, it is the Celtic spring festival*. Sacred to Brighid and associated with birth. It falls 9 months after the fertility festival of Beltaine.
I is for Ixitxachitl. Ixitxachitl isn't the only I monster, but it is one** of the most confusing. What the hell is it supposed to be? An Aztec stingray? They get a vampiric variant too? I guess I understand the need to scramble for undersea encounter type monsters, but this one makes EGG seem like he was smoking crack.
*The British Isles and western Europe have a gentler climate than the US and Canada, so the beginning of Spring is earlier.
**Irish Deer being the other one. I mean, is Ireland also in the World of Greyhawk? Every other fantasy world? Wasn't there a less obvious scientific name he could have used?