Thread title. The 2010's were a decade consisting of 10 years, with a whopping 3652 days between them. And likely had more game releases than the amount of days, maybe by more than a little bit.

Umm, yeah. Bosses! Bosses are cool, except when they're not. But this thread is here to talk about the cool ones, so all of the ones here are cool! You don't need to write down a full top 10 I guess, and you don't have to put them in order, but it's always cooler when people do that!

Just please, if your list includes final bosses or other spoilery stuff, mark it as spoiler and say what games your list spoils! Or else, just type something generic like "Final Boss from that game".

Just finished mine, guess I'll get things going.

Spoilers for Hollow Knight, Skyward Sword, Astral Chain, Metroid: Samus Returns, and Persona 5! Enter at your own peril!

In case you didn't know, I like Persona 5

I don't know if I can come up with 10, but here's the ones I liked best:

- DJ Octavio (Splatoon)

- Garm (Hellblade)

- Valravn (Hellblade)

Off the top of my head.

True final boss - Kirby Star Allies - If not the best, damn near close to being the best fight of my life, an spectacle, a challenge and a culmination of over 20 years of the deepest lore.

Bowser final fight - Super Mario 3D World

Tiki Totem - The Messenger

Zu Pharg - Xenoblade Chronicles X

Bashmaster the Unbreakable - Donkey Kong Country Tropical Freeze

Final boss - Fire Emblem Fates Conquest - I hate that boy, but god damn he gave me one of the best fights in Fire Emblem, an archer of all things.

Final boss - Pikmin 3

Urizen 3 - Devil May Cry 5 - Game should have ended here.

Dragorren - Little Town Hero

Pacifist ending fight - Undertale

Feel bad leaving out a lot of other awesome fights, but this will do.

I'll try my hand at it.

- Emperor Oblivion - Bravely Second. *And I mean the first official fight by that not the scripted one right at the beginning.

- Kenji - Shin Megami Tensei IV. Pretty much the last great test the game throws at you before the easier final part of the game (if you don't go for the neutral ending)

- Bowser Final Battle - Super Mario Odyssey. A great setup storywise goes to one of best actual fight vs is longest rival. Also JOJO fans rise up !

- Antasma - Mario & Luigi : Dream Team. A great conclusion to the dream sequence of the game against an antagonist who just got betrayed and in desperation throws himself at you. Also have some of the hardest patterns to read I'd say.

- True Final Boss - Kirby Star Allies. Wraps up nicely more than 25th year of history in one of the most somber fight of the whole saga + BIG LORE REVEALS !

- Malos Last fight - Xenoblade 2: Torna the Golden Country. Love the "timed" mechanic of this fight and what goes in the background whist fighthing. Monolith Soft knows how to do spectacle without withdrawing any control from the player.

- The Diggernaut - Metroid Samus Returns. Best and most challenging fight of the game I'd say. Almost plays like something from a Dark Souls game,lol. (Yeah, you gonna die a few times on this one)

I'll have to think about this one but they'll probably be a lot of Hollow Knight.

Not counting any monster from MHW as "boss fights", since I could easily fill this list with those fights

10.- Bloodless - Bloodstained
9.- Sword Saint Ishin Ashina - Sekiro
8.- Sigrun - God of War 
7.- Mantis Lords - Hollow Knight 
6.- The Nameless King - Dark Souls 3
5.- Gehrman the First Hunter - Bloodborne
4.- Grun - Nier: Automata
3.- The Hollow Knight/Pure Vessel - Hollow Knight
2.- Beauvoir - Nier: Automata 
1.- Lady Maria of the Astral Clocktower - Bloodborne

Honorary Mentions
Dark Beast Ganon - Breath of the Wild
Ludwig - Bloodborne
Slave Knight Gael - Dark Souls 3
Urizen - Devil May Cry 5
Alraune - Bayonetta 2
Cornell - Lords of Shadows
A bunch of others, they keep coming... 

Honestly, I think I could also make this list about Bloodborne alone, those are some of the boss fights I've enjoyed the most this last decade. Most of them are very memorable. 
Ill maybe edit later if I remember any other worth to make the list, this were the ones that came to mind. Theres many.

yikes

Well, I did enjoy it quite a bit, I felt it had one of the more epic atmospheres of any Zelda game boss fight, even if the fight itself was a bit easier than I had expected. I probably should clarify I mean the full fight with Ganon, not just the final phase as the Dark Beast tho. 

Not even sure if I can name 10 but -

Nightmare King Grimm - Hollow Knight
Sans - Undertale
Tartar - Splatoon 2 Octo Expansion