If I attack with a Gifted Aetherborn (2/3 deathtouch and lifelink) and my opponent blocks with a creature that's a 3/3 (no abilities), does my Gifted Aetherborn die?
Without deathtouch it would, but since the Gifted Aetherborn only needs to deal 1 damage to kill the other creature, he should live, correct?
Both creatures receive lethal damage and as a result die.
In the Comprehensive Rules it says the following regarding deathtouch:
702.2b A creature with toughness greater than 0 that’s been dealt damage by a source with deathtouch since the last time state-based actions were checked is destroyed as a state-based action. See rule 704.
So according to this rule any creature that get deathtouch damage gets destroyed.
But who gets to deal damage first? Is the the deathtouch creature? Is it because he only has to do one damage to do lethal damage? Let's find out in the next paragraph!
510.2. Second, all combat damage that’s been assigned is dealt simultaneously. This turn-based action doesn’t use the stack. No player has the chance to cast spells or activate abilities between the time combat damage is assigned and the time it’s dealt
So the 2 damage from Gifted Atherborn and the 3 damage from a 3/3 creature is dealt simultaneously resulting in them both perishing.
If you want to destroy the enemy creature with combat damage before it kills your creature you should take a look at first strike and double strike.
510.4. If at least one attacking or blocking creature has first strike (see rule 702.7) or double strike (see rule 702.4) as the combat damage step begins, the only creatures that assign combat damage in that step are those with first strike or double strike. After that step, instead of proceeding to the end of combat step, the phase gets a second combat damage step. The only creatures that assign combat damage in that step are the remaining attackers and blockers that had neither first strike nor double strike as the first combat damage step began, as well as the remaining attackers and blockers that currently have double strike. After that step, the phase proceeds to the end of combat step.
Both creatures die, including your Aetherborn.
Damage is dealt simultaneously and in full in the combat damage step. Then, once combat damage has been exchanged, we check which creatures have lethal damage marked on them. In this case both die: your 2/3 Aetherborn has 3 damage marked on it, which is lethal damage, and the 3/3 has damage marked on it from a source with deathtouch.
There isn't a "point race" or anything — your Aetherborn doesn't get to survive on account of needing to deal less damage to kill the other one. We don't zoom into combat in that much detail. If there was such a point race, nothing would ever kill a deathtouch creature with more than 1 toughness, since it would always outlive the other creature. Thankfully deathtouch isn't quite that powerful.
Your Aetherborn would survive if it had first strike or double strike and the 3/3 had neither, because it would deal lethal damage to the 3/3 during the first strike combat damage round, killing it before the 3/3 had a chance to deal damage back. This makes first strike & deathtouch (such as on Ankle Shanker) a pretty hard combination to deal with.
You can see the steps of the combat phase outlined in the very last page of the Basic Rules (pdf), or read further guidance about them (and the full comprehensive rules) on the MTG Wiki page for the Combat Phase and the pages for each step which it links to.
The fact that your Gifted Aetherborn only has to deal 1 point of damage to kill doesn't matter for him living or dying from combat, what matters is how much damage he takes, and without First Strike or Double Strike involved, all damage is dealt at once.
For sake of argument lets say your opponent has a Hill Giant, that's the most common card used as an example of a 3/3 with no abilities.
The combat would work like this:
Even though Gifted Aetherborn only needs to deal 1 damage to the Hill Giant to kill it, the Aetherborn still needs to assign all its damage, so it assigns 2 damage to the Giant. (If it had trample, one damage could be assigned to the giant and one to the player.) The blocking Giant then needs to also assign all its damage to the attacking creature(s) it blocked, so it assigns 3 damage to the Atherborn. Then after this assignment all damage is dealt at once, 2 damage is dealt to the Giant, which is more than the 1 needed to kill it and 3 damage is dealt to the Atherborn, which is enough to kill it. Both of these creatures then die due to damage.
If either creature (but not both!) had First Strike or Double Strike, they would hit before the other creature, say if your Atherborn had been enchanted with Siege Modification, then it would be a 5/3 with First Strike, Deathtouch, and Lifelink. It would assign and deal all 5 damage to the Hill Giant before the Giant had a change to hit back, killing the giant, there would be no hit on the Atherborn, what would have hit it is dead already.
This is why first strike and deathtouch together are a very powerful combo, as is deathtouch and trample, one kills without getting killed, the other kills and keeps going to hit the player with whatever is left over damage wise!
