RJSmalls said:
Let's face it - if you don't have a supernatural or magical means (tremorsense, blindsight, see invisibility, etc.) you're at a severe disadvantage. Let me repeat the operative words: severe disadvantage.
Again, I don't want to metagame against my party and now have every BBEG have some sort of see invisibility capability.
First, you are absolutely correct. Haste/Improved Invis/Fly is The Combo. Wait, let me correct myself -- Haste/Improved Invis/Fly/Polymorphed into a Troll or Stone Giant is The Combo.
It's been well established that in a World That Makes Sense, just about anyone who is friends with a 7th level spellcaster would walk around as a Troll or Stone Giant if they regularly adventure at all. The advantages are just too great. I have a difficult time imagining a world in which all adventurers walk around looking like giants or trolls (or night hags), but there you go.
You've got a similar problem with Improved Invis. The problem is twofold:
1) Lame-ass monsters with no magical abilities
2) NPCs
With lame-ass monsters . . . not much you can do. Give more creatures blindsight, perhaps. (Scent kind of sucks as an Invisibility Killer).
With NPCs . . . well, the main thing you have to do is get over this "fear of metagaming". In any world in which invisibility is so common, not only are all NPCs going to know it and expect it, but they'll have created well-known countermeasures. It's not metagaming for NPCs to have Wands of Glitterdust, for example, or other magic items that'll combat invisible creatures.
Hell . . . in my opinion, one of the biggest holes in the DMG list o' magic items is the absence of a Ring of See Invisibility. Not only should this magic item be existent, it should be COMMON among merchants, high-level guards, and anyone else who knows anything about how much damage that 2nd level spell can do.
Price it at maybe 10k . . . and make it relatively common among the elite. That's what I've done. (It'd be about as common as +2 weapons.)
That's not metagaming. That's common sense.