This is a very good point. If you front-load your monsters with single-use, "shock and awe" abilities, you can terrify the players and make them fear for their PCs' lives even though the monster has, in reality, shot its wad. This has the added benefit of not requiring you to fudge anything at all.One way is to hammer the party's weaknesses early on, with limited-use BBeG abilities, creating the proper terror, then, as the party recovers, give them the chance to shift the battle to favor their strengths, instead...
A good example of this was an encounter I ran between an 11th-level party and a lich. The player of the cleric wasn't there that night (another player was running his PC), so I had the lich target the cleric with power word kill on the first round. The lich said "Die," and the cleric fell over dead without a saving throw.
The lich only had the one 9th-level spell slot, and its other spell options weren't nearly so deadly, plus the PCs had defenses against a couple of the big ones. The party wasn't in all that much danger after the first spell. But boy, you sure wouldn't have known it from their reactions.
