GIANT TICK: Giant ticks first appeared in Supplement I: Greyhawk. They've changed very little, with just a few minor stat changes and clarifications to their abilities. Their major attack is to attach to their victims and drain their blood. Originally the tick drained 4 hit points per round, but now it will drain from 1-6, and become sated when the amount drained equals its total hit points; in the earlier version the tick would simply drain blood until the victim was dead. Ticks can still be removed by killing or burning them, but a new method has been added here: immersing them in water. Giant ticks still pass on a fatal disease to anyone whose blood they drink, but whereas before the disease was automatically passed on, now there is only a 50% chance. Supplement III: Eldritch Wizardry established that the disease ticks pass on is called spotted fever, and gave some extra rules regarding it. None of these additions appear here in the Monster Manual.
Armor Class: Old - 4, New - 3; Hit Dice: Old - 3, New - 2 to 4
TIGER: This is the first proper stat-block for tigers, as they've only appeared so far in the wilderness encounter tables from Supplement III: Eldritch Wizardry. They're surprisingly strong, with 5 Hit Dice and three attacks per round. In addition they're really hard to surprise, and if both of their claws hit in a single round they get two more attacks with their rear claws.
SABRE-TOOTH TIGER: Sabre-tooth tigers were first shown in the random encounter tables in the OD&D boxed set, and they also got attack and damage scores in Supplement I: Greyhawk, despite never having been properly outlined. They pretty much function as a stronger version of the tiger, having the same abilities with more hit points, and an attack bonus due to their over-sized teeth.
Damage: Old - claws 1-4 and bite 1-12, New - claws 2-5 and bite 1-12
TITAN: The existence of titans was rumoured in the OD&D boxed set, and they got their first stats in Supplement I: Greyhawk. They were powered up in Supplement III: Eldritch Wizardry, gaining psionic powers, magic resistance and a tendency to pal around with storm giants. They retain all of their considerable abilities here, including psionics, magic resistance, and the ability to cast cleric and magic-user spells of up to 7th level. In addition, they gain the following abilities: invisibility, levitation and etherealness, all at will.
Originally, titans were able to cast protection from magic at double strength. Except for one problem: there is no such spell. That's been amended here to protection from evil, and it's only double strength against Lawful Evil creatures.
I'm somewhat disappointed to note that the bit about there only being ten titans in total has not made it into the Monster Manual. We;re also back to referencing real-world places, with the garb of titans being described as "Grecian".
This one is a little difficult to figure out, because of the way titans are set up. Originally they had an Armor Class ranging from 2 to -3, hit points ranging from 75 to 100, and a Movement that was usually 15", except for a 10% minority that moved at 21". It's been codified a lot better in the Monster Manual, with a roll of 1d6 determining the AC and HD of the Titan. AC still has the same range, but now Titans have between 17 and 22 Hit Dice. Those with smaller Hit Dice have the higher speed, and the stronger ones have a higher damage range.