I made a final boss themes suggestion to the guy who make all of those Epic Final Boss Battle Theme Collections, and he confirmed that he'll take my suggestions into account.
Here's my entire YouTube comment:
Can you do the following final boss themes for your future Final Boss Collections (in no particular order):
Sonic Heroes - What I'm Made Of
https://www.youtube.com/watch?v=8mOoYDTn-Bk
Sonic Adventure 2 - Live and Learn
https://www.youtube.com/watch?v=dGIIei8Yusk
Sonic Adventure - Open Your Heart
https://www.youtube.com/watch?v=DRlbbpWTC9g
Donkey Kong Country - Gangplank Galleon
https://www.youtube.com/watch?v=CAMVWQjrPcs
Donkey Kong Country 2 - Crocodile Cacophony
https://www.youtube.com/watch?v=BeOFISPLBss
Donkey Kong Country 3 - Big Boss Blues
https://www.youtube.com/watch?v=WrCEtuuVHC0
Donkey Kong Country Tropical Freeze - Volcano Dome
https://www.youtube.com/watch?v=P3dmr_cFLqg
Mario Party 3 - Stardust Battle
https://www.youtube.com/watch?v=u9z0XkojHLQ
Pokemon Omega Ruby Alpha Sapphire - Deoxys Battle (Deoxys is the True Final Boss story-wise in the postgame Delta Episode)
https://www.youtube.com/watch?v=oc7cgyac4S0
Super Mario RPG - Fight Against Smithy, Who Likes Transforming
https://www.youtube.com/watch?v=a8xRPcSgOgU
Paper Mario - Bowser's Rage
https://www.youtube.com/watch?v=ZmieSS7znCE
Paper Mario - King of the Koopas
https://www.youtube.com/watch?v=w5AZRtpTLhM
Mario & Luigi: Superstar Saga - Bowletta Battle
https://www.youtube.com/watch?v=3iXKaVDesnA
Mario & Luigi: Superstar Saga - Final Cackletta Battle
https://www.youtube.com/watch?v=_rg2QdJbTzw
Paper Mario: The Thousand-Year Door - Shadow Queen Phase 1 (Peach Form)
https://www.youtube.com/watch?v=8wU2RcvmEbg
Paper Mario: The Thousand-Year Door - Shadow Queen Phase 1 (True Form)
https://www.youtube.com/watch?v=1YUjZUqlEY8
Paper Mario: The Thousand-Year Door - Shadow Queen Phase 2
https://www.youtube.com/watch?v=GFsm1x0fQQU
Open Season (The Game) - Shaw Showdown
(Can't find a standalone video of the theme, but it's epic and country-style, which makes sense)
Super Smash Bros. for the 3DS/Wii U - Master Core
https://www.youtube.com/watch?v=Dn0U32CQ9U8
Super Mario 64 - The Ultimate Koopa
https://www.youtube.com/watch?v=TLXBKmwl250
Sonic and the Black Knight - With Me
https://www.youtube.com/watch?v=LNsGT2Pjug8
Final Fantasy 7 - One Winged Angel
https://www.youtube.com/watch?v=YwbMGAM2W38
Pokemon Heartgold Soulsilver - Red/Lance Battle
https://www.youtube.com/watch?v=H2ijQXqxa64
Pokemon RSE - Steven/Wallace Battle
https://www.youtube.com/watch?v=Vq2Evw5UBvU
Pokemon Omega Ruby Alpha Sapphire - Steven Battle
https://www.youtube.com/watch?v=yaarE0mO09A
Pokemon Mystery Dungeon 2 - Darkrai Battle (Final Boss of postgame, use the same battle theme as Dusknoir)
https://www.youtube.com/watch?v=K50K47NXDkU
Pokemon Diamond/Pearl/Platinum - Cynthia Battle
https://www.youtube.com/watch?v=0JkqQ_kLxUM
Sonic Generations - Time Eater (Classic Version)
https://www.youtube.com/watch?v=7QXR2xv5Mi0
Sonic Generations - Time Eater (Modern Version)
https://www.youtube.com/watch?v=9Obo81P4V_4
Pokemon X/Y - Diantha Battle
https://www.youtube.com/watch?v=9O-c2YZTvH4
Pokemon Black2/White2 - Iris Battle
https://www.youtube.com/watch?v=e8OyQ2Wu9es
Pokemon Black and White - Ghetsis Battle (The champion, Alder, can only be fought postgame. These are the only two Pokemon games that do that)
https://www.youtube.com/watch?v=nX2hOoaLb4Y
Pokemon Black and White - Final N Battle (can be considered phase 1 of the final battle, since Ghetsis is fought immediately after him)
https://www.youtube.com/watch?v=u2GeWOMgxiE
Pokemon Black and White LAST BATTLE -N^n mix (N Final Battle Remix) (This isn't heard in-game, but it is part of the official soundtrack.) https://youtu.be/Ty4Visacyc4
Super Mario Sunshine - Bowser Battle
https://www.youtube.com/watch?v=ECIv3Mew4L8
Epic Mickey - The Phantom Blot
https://www.youtube.com/watch?v=RD1hHX59sPg
Castle Crashers - Necromancer Battle
https://www.youtube.com/watch?v=sJmwooRTpfo
Alien Hominid - Final Battle
https://www.youtube.com/watch?v=5iAUOuF0h7c
Crystal Story 1 & 2 - The Shattered Sky
https://www.youtube.com/watch?v=tRlNN7dbmKs
MARDEK 2 & 3 - Governance de magi Battle