AD&D Monster Manual part 51

STAG and GIANT STAG:  Stags have only appeared previously in the Wilderness Encounter tables from Supplement III: Eldritch Wizardry, and giant stags have not appeared at all.  There's honestly not a lot to say about either of them.  Regular stags wander around in herds which they protect aggressively.  Giant stags do the same thing, only giant-er.  I'm all in favour of having regular animals in the Monster Manual, but they don't always make for the most compelling entries.

STIRGE: Stirges first appeared in Supplement I: Greyhawk.  These weird bird-mosquito hybrids have long been the scourge of low-level adventurers everywhere: a 1 hit-die monster that hits like it has 4 hit dice, and attaches to its victims to suck their blood.  They appear in large numbers as well, just to add to their deadliness.

In general they're another case of Gary being pretty happy with his previous work, but there are a few minor statistical changes as noted below.  The most significant of these is the addition of a speed for when they are grounded, and also a limit to how much blood they can drink.  Previously a stirge would keep drinking until its prey was a bloodless corpse; now it will drink until it has drained 12 hit points, before flying away to digest.  The only notable omission is a method for detaching a stirge from its victim while it is drinking their blood.

There isn't too much for me to explain away here.  The new stirges are slightly bigger (thus explaining both the extra hit point and the slightly worse Armor Class), but they don't drink quite as ravenously.  Again, I will go back to my old stand-by excuse: the previous version of the stirge was not quite fully grown, and still in need of lots of blood in order to fully mature.  The Monster Manual version is fully mature, and doesn't require quite the same amount of sustenance.

Stat Changes:
Armor Class: Old - 7, New - 8; Movement: Old - 18", New - 3"/18"; Hit Dice: Old - 1, New - 1+1

Brother, you been STIRGED.

STRANGLE WEED: Strangle weed was first detailed in Supplement II: Blackmoor, but here it gets a complete overhaul.  Conceptually it hasn't change a bit; it's still seaweed that grabs and constricts anything that gets too near.  However, the Supplement II version of strangle weed had a method of resolving that constriction that didn't take the victim's Strength into account at all.  In the Monster Manual it's been changed completely.  Each frond of the weed gets its own Strength score; if the victim's Strength is higher he gets a chance to escape, and if it is lower he takes crushing damage.  He can still try to hack his way to freedom, but with a -2 penalty to attack.  Multiple fronds can grasp a character, and their Strength scores are added together.

The original strangle weed had an Armor Class of 1 and 12 Hit Dice, which is actually pretty tough.  The new version has Armor Class 6 and 2 to 4 Hit Dice (presumably for each frond).  It's a major difference in power, and I'm willing to chalk these up as two different yet similar species.  The original version is obviously made of much sterner stuff, and possibly injects its victims with a poison that negates their strength.