"Some other techniques I've witnessed being used, with varying success, include:
- fudging enemy stats in combat (ie monsters mysteriously drained of part of their remaining hp at some point)"
Never done this that I can recall. I think it's ok for DMs to do this if it's a new, not previously encountered NPC or monster. But after an epic battle and narrow victor, don't tell the players afterwards (as a DM of mine once did) "Of course that Yuan-Ti actually had 48hp, I reduced it to 28hp so you wouldn't die"
"- enemies suddenly fleeing, with or without good reason to do so (which doesn't mean that every withdrawal from combat is fudging of course, not evryone likes to fight to their deaths as a routine action);"
It needs to be reasonable in-game. When PCs IMC first encountered Harecules, he didn't treat them seriously and didn't pursue when they fled. Over the years he's come to take threats much more seriously. I'd say NPCs retreating in the face of a rugged defense is almost always plausible if they would probably win eventually but with very heavy losses. Usually however if the PCs are losing, I expect them to know when to run away or die fighting.
"- NPCs riding to the rescue out of nowhere, horns blowing (shudder);"
Early IMC two NPCs ('Red' Ivy & Bear the Barbarian) rescued the group from some Gaxmoor gargoyles - the group had no magic weapons. I think I had the whole encounter pre-planned though, including the NPC intervention. I think this is fine if done in moderation and in plausible circumstances.
"- crit rules suddenly forgotten or remaining mysteriously un-applied when they'd have gone against a PC instead of in their favour."
Never done this. I don't see misapplying the rules as within the DM's prerogative, whereas deciding NPC actions certainly is.
"As a player, I'm generally frustrated when I notice things like that going on. I don't rely on a high PC death rate to enjoy a game (whether I play in it or run it), but if I feel that my PC is in some sort of "god mode" I feel cheated out of half the fun."
Me too. For D&D, maybe 3/4 the fun. I'd be more accepting in Feng Shui or the Buffy RPG. D&D is dependent on risk more than theatrics IMO, other games emphasise theatrics more and have resolution mechanisms to support this.
"And I say that after recently having lost three PCs in three consecutive sessions, at least one of which I'd invested a great deal of background and RP effort in."
Er, yeah, sorry about that...
"One of the safer ways to minimise PC deaths is, of course, to tone down challenges. Again, if you have players out for some tactical challenge, you may find you're providing a rather luke-warm game. "
Giving players what they want, inasmuch as it coincides with what the GM desires, is always good.
"BTW, I'm not sure what avoiding the use of a battle grid has to do with minimising PC deaths. In my experience with DnD, it's the other way round: visual representation of a combat situation helps minimise misunderstandings - if you take care how you position yourself, you're less likely to get killed through not understanding what is where."
I agree - the battle grid definitely cuts down on casual or accidental PC deaths. It seems to give weaker PCs much more opportunity to contribute through good tactical play.