Ahhh this Death Battle, safe to say that no one liked this one. However after a while of going through some debunk videos again I noticed that many people were just on the Buu side of the argument and not the kirby side of the argument. Many people just debunked the claims about Buu not being FTL, him breaking into pieces when a planet was destroyed and how he should have been able to absorb characters since Kirby did and then were like boom Buu stomps.

However that's wrong. Screwattack downplayed both characters, they downplay characters all the time, it's not a thing exclusive to dragon ball, or anime, it's for pretty much anyone they talk about.
On top of that Kirby has gained new impressive feats since then as well. So let's begin starting with Buu and I'll use the skinny Buu in DBS for this fight since he's the most recent one.

Attack potency
Multi Galaxy - Universe level



Buu should be on this level for being able to fight Goku who almost destroyed the universe in his clash with Beerus. While it is possible that Goku was holding back (and more likely as well) I'm just gonna say that Buu is on this level in anyways.

Now getting Buu's top speed is a bit tricky though I think I have a good idea on how to do it. Buu was going to destroy galaxy to Galaxy and eventually reach supreme Kai and elder Kai. Meaning most likely he'd reach the elder Kai before he died. The lifespan of a Kai according to Akira toriyama is 75,000 years, while there are some inconsistencies with that number lets just go with that.

Let's say the elder Kai has already lived for 70,000 years so he has 5,000 left to go. There are about 100,000 light years in a Galaxy and about 2 trillion galaxies in a universe

From all of that we get Buu to be.

40, 772, 802, 971, 591, 434, 000

Over quadrillion times faster than the speed of light (however this is a massive high ball as buu hasn't shown anything close to this but oh well.

Abilities

Master Martial Artist, Superhuman Physical Characteristics, Magic, Ki Manipulation (Can be used defensively and offensively, to strengthen his skin or to fire ki blasts, which can home in on targets, and form defensive barriers), Ki Sensing (Can locate others by reading their ki), Flight, Telekinesis, Absorption (Can absorb others to gain their abilities and knowledge, increasing in power as well), Body Control (Due to his body's elasticity and amorphous nature, Buu can control it as he pleases), Duplication (Can split into distinct bodies and individuals through fission), Elasticity, Shapeshifting, Power Mimicry (Buu can copy techniques after seeing them once, copying Goku's Kamehameha and Kibito Kai's Kai Kai), Afterimage Creation, Air Manipulation (Can exhale with enough force to cause severe, powerful winds), Healing, Transmutation (Can turn people into candy and other types of food), Teleportation, Portal Creation (As Super Buu, he can scream with enough force to rip open holes in dimensions, allowing him to travel across space and time), Resistance to Poisons and Mind Manipulation (Babidi cannot reliably control Buu through any means despite the evil in his heart), Immortality (Types 1 and 3), Regeneration (Mid-High; Buu can regenerate from being reduced to vapor)

Now for Kirby.

Attack potency
Multi universe level

Kirby defeats a guy who seemingly uses a universe as a weapon that clearly has Stars and galaxies and so on. Kirby can damage this guy fairly easily.

Hyness is confirmed to be multi universal level and Kirby scales to him so Kirby should also be on this level.

It's also backed up by this. Not to mention Kirby has taken on many characters that have warped alternate universes and so on. So yes Kirby should indeed be on this level.

Speed

Kirby has shown to be comparable to the speed of his warp star as he's fought many characters with and without it. So we should be able to compare his normal speed to the speed of his warp star which from this Calc can go over Quandrillion times faster than the speed of light. Kirby has also fought characters that can go the speed of his warp star so this goes for fighting speed as well.

https://plus.google.com/+ChanceSchulz/posts/PkBk5fGcKu6

 Superhuman Physical Characteristics, Magic (By himself or copy abilities), Flight (Whether through his own abilities, copy abilities, Warp Star or Starship), Enhanced Senses, Can harm intangible beings & souls, Useful fighting style, Elasticity, Can turn into a limbless ball, Transmutation (By himself, Cook, Baton, Bubble, Magic, and with Robobot Armor), Power Absorption (Upon contact), Duplication (By himself, Mirror, and with Replica), Warp Star Creation, Vehicular Mastery, Universal & Dimensional Travel (with Warp Star & magic sock), Empathic Manipulation, Cloth Manipulation(Can create clothes for him or others), Can turn into a small ball of intangible energy, Can shoot out small air puffs (enhanced under the effects of the Mint Leaf & Big Air Bullet Boost Orb), Energy Projection, Danmaku, Telekinesis, Summoning (Can create Helpers from Copy Abilities. Can summon Animal Friends, Dyna Blade, an army of Gators, the Warp Star [naturally or calling it with his cell phone] or the Starship. Can summon a meteor to do massive damage and stun his enemies[after collecting 4 Power Tablets, which appear just by hitting his opponents a certain amount of times]. Can summon other Kirbys with his phone [Amazing Mirror only]), Longevity, Immortality (Type 3), Regeneration (At least Low-High, likely Mid-High, Low-Godly as Ghost Kirby; Can throw off half of his body, regenerate from being shattered, and from being popped as Balloon. Should be equal to Shadow Kirby, his Mirror World counterpart. Ghost Kirby recreates his body from nothing after absorbing life force), Resurrection (Can resurrect others naturally. Can resurrect himself with Reviving Tomato [It only works once]. When dead, he can transform into Ghost Kirby to absorb some Life-Force from an enemy upon contact and resurrect.), As Ghost Kirby he also has the following powers; Teleportation, Intangibility, Immortality (Type 7) & Immunity to Death Manipulation, Breaking the Fourth Wall, Toon Force, Attack Reflection (By himself [via Inhale & Star Spit], Mirror, Hypernova), Size Manipulation(By himself [via Star Dash], Mini, Giant Stone, and with Sparkling Stars & Jumbo Candy), Earth Manipulation (Can hit the ground to leave a fissure under his opponent), Dimensional Storage (Can store things in his stomach for later use), Can fuse enemies with copy abilities or each other, Can inhale foes and objects alike, trapping them in his stomach, an infinite parallel dimension to either spit them out as projectiles (normally turning them into star shaped energy bolts in the process) or copy their abilities by manipulating the space in stomach, giving him new abilities such as the following; Elemental Manipulation (Fire, Ninja, Ice, Spark, Plasma, Leaf, Tornado, Water, Metal, Volcano), Weapon Mastery (Sword, Hammer, Archer, Spear, Cutter, Parasol, Stick, Whip, Yo-Yo, Explosive Shuriken, Dynamite, Needle, etc.), Holy Manipulation(Doctor Healmore), enhance Martial Arts(Backdrop, Fighter, Throw, Ninja, Smash, Suplex), Forcefield Creation (Spark, Ice, Needle, Smash, and with Prism Shield), Statistics Amplification (With items and Final Weapons. Durability Augmentation [Stone, Metal], Speed Augmentation [Jet, Wheel]), Gravity Manipulation (UFO), Energy Manipulation and Projection (Beam, UFO, Crash, etc.), Darkness Manipulation (with Dark Matter Blade), Light Manipulation(Light, Water, Rainbow Sword), Love-Based Attacks (Love-Love Stick), Invulnerability(Stone, Metal, Wheel, Fire, Hi-Jump, and with Invincible Candy, Jumbo Candy & Metal Boost Orb), Sound Manipulation(Mike, Bell, and with Microphone), Teleportation (ESP, and with Warp Panel, Better Telekinesis & Precognition (ESP), Afterimage Creation (Ninja), Poison Manipulation (Doctor and Poison), Acid Manipulation (Poison), Corrosion Inducement (Poison) Magnetism Manipulation (Electric Stone), Transformation (By himself, Wheel, Missile, Balloon, Ball, etc.), Summoning (Magic [Can call upon Meta Knight]), Animal Mimicry (Animal, Beetle, Wing), Life Manipulation(Magic), Intangibility, Immortality (Types 6 & 7), Invisibility, Self-Resurrection, Existence Erasure and Possession (Ghost), Extended Power Mimicry (Copy), Status Effect Inducement (Balloon, Ice, Spider), Thread Manipulation (Spider), Illusion Creation (Kabuki), Time Stop (Beam Mage), Information Manipulation, Data Manipulation, and Information Analysis (Via Copy, Robobot, and Halberd Mode, which scans opponents, reduces them to computing data, and absorbs their information), Homing Attack (Cutter [via Hyper Cutter], Tri-Missile Attack), Void Manipulation (Hypernova; those swallowed don't go to the stomach dimension, and are instead deleted entirely), Explosion Manipulation (Bomb, Ninja, and with Balloon Bomb, Cracker, Timed Dynamite, Action Star [Can cause all opponents to explode, dropping health to one point] & 3D Helmet Cannon), Sleep Manipulation (Sleep [self-induced], Ninja, Doctor, and with Action Star), Stealth Mastery (Mini, Ninja, Archer, Leaf), Bubble Manipulation(Bubble), Food Manipulation (Refrigerator), Paint Manipulation (Paint), Balloon Mimicry(Balloon), Portal Creation (Shard Gun), Healing (Refrigerator, Doctor, Sleep, and with Action Star, Maxim Tomatoes & Maxim Tomato Boost Orb), enhance Body Manipulation (Cutter, Needle, [Kirby 64 versions]), Spin Dash (Needle), Invisibilitywith Invisibility Stone & Invisibility Boost Orb, Intangibility with Invisibility Stone, Anti-Support with Action Star (Can decrease the speed and jump of his opponents), Divine Weaponry with all Platinum Armor & Weapons, Limited Probability Manipulation with all Armor and Weapons (Increases the materials gain at the end of the battle), Day and Night Manipulation with Day and Night Switch, Enhanced Thievery with Cashgrabber Boost Orb (Increases the number of things he can steal from enemies), Limited Automatic Mobility with Deflector Boost Orb, Berserk Mode with Berserk Boost Orb, Able to use his Copy Abilities naturally, Resistance to Reality Warping, Magic, Possession (Multible characters with this power were unable to possessing him), Transmutation (While he has been transmuted several times, he always kept his consciousness and at least his basic functions. Can avoid being spit as a star by other Kirby and being turn into a star by Keeby, who shares Kirby's power to turn enemies into stars by hitting them.), Existence Erasure (Got hit by Drawcia's deletion wave and survived quite easily. Can fight Necrodeus when reduced to fractions of himself), Gravity and Radiation Manipulation (Withstood black holes numerous times), and Spatial Manipulation(Survived multiple space-based attacks from the likes of Marx, Magolor, Galacta Knight), and Mind Manipulation (Unaffected by Magolor controlling the inhabitants of the universe. Also defeated Taranza and Dark Taranza despite their "hypnosis magic"), Fire, Ice and Electricity Manipulation (Resisted attacks from Dark Nebula), Immunity to Bone Manipulation(Lacks a skeleton), Can move in frozen time, Can fight without his soul in his body(though Kirby still needs it to exist to live.)

Conclusion

Even if we high ball Buu like we did here it really doesn't matter, he can't beat Kirby, Kirby has shown far better feats. I know people like the hype up dragon ball a lot but seriously while dragon ball characters look super strong and can punch really hard they don't have these insane feats like many video game characters do.

Winner: Kirby