I have done my best to format this quickly for legibility. Forgive any errors, please.

Please note that this list is most likely incomplete and might be wrong in some aspects.

Undocumented Patch Notes - January 13, 2015

General:

• Envenom nerfed from 7 to 6 damage ticks resulting in a reduction of the total damage from 210 (+35) to 180 (+30). official patch notes state that the Core would do 20% more damage versus Heroes. This is wrong. The Core's damage is still at 220 per second, it did not change.
• Healing Totems might only die from auto attacks and several abilities like Tyrael's Q "El'Druin's Might" again
• Calldown MULE can now be cast using the minimap

Golem changes:

• now detect MULES within a range of 12, if on lane
• added potential bug: their cast range is 8, will they walk there? Usually, the MULE should be out of the Golem's vision range of 8, but why is the detection range 12 now?

Grave Golem:

• root impact damage buffed from 30 to 100 and now deals 100% bonus damage against minions, summons and structures (although root cannot hit structures)
• root damage over time buffed from 15 to 50 and now deals 100% bonus damage against minions, summons and structures (although root cannot hit structures)

Haunted Mines Underworld Boss:

• root impact damage buffed from 30 to 100 and now deals 100% bonus damage against minions, summons and structures (although root cannot hit structures)
• root damage over time buffed from 15 to 50 and now deals 100% bonus damage against minions, summons and structures (although root cannot hit structures)

Haunted Mines Summoned Golem:

• root impact damage now deals 100% bonus damage against minions, summons and structures (although root cannot hit structures)
• root damage over time now deals 100% bonus damage against minions, summons and structures (although root cannot hit structures)
• stomp damage has been lowered from 300 to 35 and now deals 100% bonus damage against minions, summons and structures
• added potential bug: while being killed by a special MULE-killing ability, MULES might still be able to repair ammunition, but not life

[Ed: Some general notes added in right here.]

• Forts and Keeps can't add a slow to dead units anymore (e.g. Uther and Tyrael)

• cleaned up a lot of timescale settings which could potentially have caused problems with Void Prison

• if you write "gg", "gg!", "GG" or "GG!" after the Core dies, it will be displayed to all players (max one chat message per player)

• mercenaries are now invincible for 3 seconds during their camp-spawning animation

• abilities that cause a hero to attack a target after ability execution are now verifying that you don't have orders queued

• the year of the official patch notes for this patch has been decreased to 2014 from 2015 in the battle.net app

Maps:

Cursed Hollow:

• curse spawn point pattern changed:
• second tribute of the map spawns in a different column than the first one
• third tribute follows the spawning cycle's third step: spawn in a different column than the two previous two tributes and not three tributes after another between the same lanes
• the fourth tribute is the first step in the cycle

Abathur:

• Bolt of the Storm talent removed

Locust changes:

• life decreased from 300 (+35) to 230 (+20)
• damage decreased from 25 (+5) to 15 (+3)
• Assault Locust's explosion damage decreased from 60 (+12) to 50 (+5), weapon cleave damage from 15 (+2.5) to 7.5 (+1.5)
• Locust spawning period reduced from 20 to 15 seconds
• Envenomed Nest (talent) damage per tick increased from 4 (+1.205) to 3.5 (+1.5) [now it does what the talent states, 3 ticks and 10% of Toxic Nest's damage per tick = 30%]
• Ultimate Evolution's duration has been reduced from 45 to 30 seconds

Azmodan:

Globe of Annihilation

• Infernal Wrath's (talent) damage over time now reveals the unit
• a hit does not reveal Azmodan anymore (unverified, did it reveal him before?)
• added bug: Sieging Wrath's (talent) damage has not been increased. Thus, the Sieging Wrath talent is currently dealing too little damage unless you throw it on your own feet.
• added bug: Sieging Wrath (talent) combined with Infernal Globe (talent) deals too little damage, too.
• Demonic Invasion Zombies now have 200 (+30) life

Chen:

• Breath of Fire's damage over time is now revealing the enemy
• Storm Earth Fire's spawning duration reduced from 1.125 to 1.0

Diablo:

• Overpower's implementation changed. It might behave better/different around unwalkable areas

ETC:

• Stage Dive now impacts 0.0625 seconds faster

Falstad:

• Rewind and Bolt of the Storm talents removed (Blizzard added that to their notes already)
• added bug: Mighty Gust does not receive cooldown reduction from battle momentum

Illidan:

• Evasion is not a transient ability anymore.
• This might effect when you can cast it and when you can't while performing other abilities.
• This change might have added some sort of auto-queueing or might even allow correct execution of queuing.

Li Li:

• Ice Block talent removed
• Healing Brew's range decreased from 8 to 7

Water Dragon changed:

• damage reduced from 260 (+25) to 140 (+14)
• splash damage was raised from 50% to 100%
• self-silence time reduced from 1 to 0.5 seconds (time that you can't cast anything else)
• slow duration increased from 3 to 4 seconds
• slow increased from 40% to 70%
• delay until the dragon launches onto a target reduced from 3 to 2 seconds

Clout Serpent changes:

• damage from 15 (+4) to 20 (+2.2)
• attack range is now 7
• attack period is 0.75
• cooldown increased from 8 to 10
• lightning serpent hop radius increased from 4 to 5
• projectile flys 3 times faster

Jug of 1000 Cups:

• cast intro time of 0.15 removed
• finish time of 0.1875 added
• delay of 0.25s until the first heal is launched has been removed
• level 20 talent Jug of 1000.000 Cups now heals two targets

Jaina:

• Water Elemental life reduced from 710 (+100) to 710 (+80)
• Water Elemental now deals Frostbitten (talent) bonus damage, too
• Arcane Intellect returns mana from Cone of Cold 0.0625 seconds after the hit

Kerrigan:

• The Ultralisk lost its creep bonus:
• Life regeneration bonus on creep reduced from 3 life/s to 0 life/s
• Movement speed bonus on creep reduced from 20% to 0%

Malfurion:

• Tranquility can now heal heroes within Ice Block

Muradin:

• Muradin's Avatar bonus life improved from 500 (+75) to 320 (+96)

Nova:

• Blood for Blood talent removed from Nova
• Holo Decoy cast range increased from 6 to 8

Triple Tap's missile blocking area during the missile's launch has been changed: * arc reduced from 90 to 45 * radius increased from 0.33 to 1.0

Rehgar:

• Farsight can now be casted on Minimap

Sgt. Hammer

• Hyper Cooling Engines buff cannot be added to a dead hero anymore (bug fix when you chose it while dead?)

Stitches:

• Gorge's damage is now dealt when the hero exits instead of on cast and on exit
• Devourer now requires the target to reach a distance of 10 during the cast to abort it instead of 1

Tychus:

• added bug: using Overkill without moving allows Tychus' weapon to still fire on the target
• Skin Variations now show decals from Overwatch characters

Valla:

Hungering Arrow changes

• initial delay before scanning for a first target reduced from 0.435 to 0.375 seconds
• second and third hit now require visible targets
• Vault's duration has been reduced from 0.3 to 0.1875 seconds

Zagara:

• The Nydus Network is not considered a structure anymore
• Devouring Maw cannot hit heroes that are mid-air anymore (=> leaping Sonya, jumping Muradin, flying Falstad)
• Envenomed Spines does not reveal the target anymore

Weird change that might not be a real change, but it is in the game data:

• Zagara's Devouring Maw had one behavior's duration reduced from 5.0 to 4.0625. But that would have ment that a hero was damaged 5 times after the initial damage and that the hero was nearly a second longer stunned. But that does not seem to have been the case.

I didn't list all changes Blizzard made. So, please consider looking into Blizzard's official patch notes in order to enjoy a more complete list: http://us.battle.net/heroes/en/blog/17345414/heroes-closed-beta-patch-notes-january-13-2015-1-13-2015#Nova

~ Ahli