1 Elecman's Theme (Mega Man) and Faithfully - Journey
2 Robo's Theme (Chrono Trigger) and Never Gonna Give You Up - Rick Astley
3 Plantation Theme (Cave Story) and Want You Gone (Portal 2)
4 Use Your Head (Earthworm Jim) and Pumped Up Kicks - Foster The People
They seem to have almost the exact same bass line.
5 Stage Select (Mega Man 2) and I Sawed The Demons (Doom)
6 Sanctuary Guardian (Earthbound) and MROB (Mother 3)
7 Dangerous Foe (Mother 1) and Sanctuary Guardian (Earthbound)
8 Baby - Justin Bieber and Friday - Rebecca Black
They are both infamously and universally hailed as the worst songs of all time, so that definitely counts. - xandermartin98
9 Chinese Food - Alison Grande and Friday - Rebecca Black
10 Fight Against Monsters (Super Mario RPG) and Normal Battle (Mario & Luigi: Superstar Saga)
11 Jenka's Theme (Cave Story) and Letkajenkka
Well, the song is literally an 8-bit arranged version of Letkajenkka, so...
12 Life Capsule (Cave Story) and Item Acquisition Fanfare (Super Metroid)
13 New Age Retro Hippie (Earthbound) and Johnny B. Goode
14 Invincibility (Super Mario Bros.) and Fever Rush Theme (Super Smash Bros. 4)
Same song actually.
15 Amalgam (Undertale) and Cave Of The Past (Earthbound)
It's literally the exact same soundfont, by the way. - xandermartin98
16 Through The Fire And Flames (Guitar Hero/Rock Band) and Moonlight Sonata Third Movement - Beethoven
17 Who Turned Out The Lights? (Earthworm Jim) and Maple Leaf Rag
18 Sky Runner (Earthbound) and Won't Get Fooled Again - The Who
19 Battle Against A Weak Opponent (Earthbound) and Tequila - Peewee Herman
20 Haunted Hotel (Super Mario Sunshine) and Battle Against A Weak Opponent (Earthbound)
21 Chykka (Metroid Prime 2) and Gandrayda (Metroid Prime 3)
22 Save Room (Kirby Super Star) and All-Star Rest Area (Super Smash Bros. Melee)
Same song actually. Masahiro Sakurai made Kirby AND Smash Bros.
23 Mr. Batty Twist (Mother 3) and the Adam West Batman theme song
24 Porky's Theme (Mother 3) and Frere Jacques
25 Modern Life (Devo) and Rocko's Modern Life (Pat Irwin)
26 Item Room Ambience (Metroid and Super Metroid)
The one in Super Metroid sounds insanely creepy, but if you pay attention you will immediately notice that it is actually just a remake of the exact same item room theme from NES Metroid.
27 Dangerous Highway (Mother 3) and Upper Brinstar (Super Metroid)
28 Lower Brinstar (Super Metroid) and Creep - deadmau5
29 Land Of The Livid Dead (Rayman Origins) and A Fistful Of Dollars - Ennio Morricone
30 Natural Killer Cyborg (Mother 3) and Beat It - Micheal Jackson
31 Hardware Store - Weird Al and "The Elements Song"
32 Hardware Store - Weird Al and Dumbledore - Unknown Artist
33 Crisis City (Sonic 2006) and The Matrix Soundtrack
34 Metallic Madness Bad Future JP Remix (Sonic CD) and Classic Crisis City (Sonic Generations)
35 Stage Select (Batman: Return of The Joker GB Version) and Stage Select (Mega Man 2)
36 Stage 1 (Rocket Knight Adventures) and Overworld (The Legend Of Zelda)
37 Ridley Theme (Super Metroid) and Battle With Meta Knight (Kirby Super Star)
38 King Dedede's Theme (Kirby Super Star) and Masked Dedede (Kirby Superstar Ultra)
39 Big Bad Baby Bowser (Yoshi's Island) and Galacta Knight (Kirby Super Star Ultra)
40 Psycrow! (Earthworm Jim) and Bizarre Love Triangle - New Order
41 Sanctuary Fortress (Metroid Prime 2) and Tidal Tempest Returns (Donkey Kong Country Returns)
42 Big Bad Baby Bowser (Yoshi's Island) and Natural Killer Cyborg (Mother 3)
43 Natural Killer Cyborg (Mother 3) and Dr. Wily Stage 1 (Mega Man 2)
44 Saria's Song (Zelda: Ocarina of Time) and Song Of Healing (Zelda: Majora's Mask)
45 Let It Go (Frozen) and Let It Snow
46 Chum Bucket Lab (SpongeBob SquarePants: Battle for Bikini Bottom) and the Terminator 2 theme song
47 Bonetrousle (Undertale) and Unfounded Revenge (Mother 3)
48 Startup (Sega MK III) and Main Theme (Space Harrier)
They're the same, basically.
49 You Can Do Anything (Sonic CD) & Green Hill Zone (Sonic 2 [Game Gear])
50 Frozen Hillside (Kirby Air Ride) & Run My Dog, Run (Mother 3)