1P-2P side differences

-No cosmetic differences, only gameplay differences

Air Gallet
starting with different bombs (the respective other ones can be picked up later)

Deathsmiles
2p: weaker bomb (https://www.nicovideo.jp/watch/sm27478219)

Dodonpachi
1p: you can continue your chain during a laser bomb when your max bonus is active
2p: 1) small star items accumulate over the course of the whole game; 2) easier 2-3 midboss with laser ship types; 3) only fast bullets during final attack of the TLB

Dodonpachi Daioujou (white label and black label)
2p: less iframes during hyper activation on bosses

Espgaluda
2p: more disc enemies / bullets during st3 midboss [in the port, both sides behave as arcade 2p side]

Esprade
2p: 1) higher starting rank; 2) killing enemies with your barrier shot increases the bonus timer

Fire Barrel
2p: life bonus after each loop is doubled, even though the game only displays a single life bonus on screen

Forgotten Worlds
different characters

G.Darius
2p: bosses have more HP

Gekirindan
2p: 1) Type C has a stronger shot; 2) lower difficulty [unconfirmed]

Giga Wing
2p: shot deals more damage

Guardian Force
Some (maybe all) weapons behave differently on the 2p side

Hotdog Storm
2p: faster movement

Ibara
different ships

Ketsui
2p: slightly lower rank, barely noticeable

Ketsui IKD Special
2p: extend glitch

Kyukyoku Tiger II / Twin Cobra II
green weapon is unique to each player side

Life Force
different order of powerups on the gauge

Mushihimesama
2p: 1) third attack of the TLB changes from aimed to random and is therefore more difficult; 2) second attack of the TLB is slightly different and has missing bullets (cf. https://youtu.be/UVAq597JFD0)

Nostradamus
different ships

P-47 Aces
2p: due to a lower spawning point on screen, you can go inside the ship on stage 4 (cf. https://www.dailymotion.com/video/x4wa8yt)

Progear
bullet sound differences (https://youtu.be/dkRGZgwfnkw)

Raiden
2p: easier difficulty

Raiden II
2p: 1) starts with cluster bombs; 2) checkpoints (Japan ROM only)

Raiden III
2p: faster diagonal movement [unconfirmed]

Raiden DX
2p: After your hitbox increases from collecting a certain number of power ups, your horizontal movement becomes faster while your vertical movement becomes slower (https://streamable.com/cll1p).

Rapid Hero
2p: lower difficulty [unconfirmed]

Salamander 2
2p: lower rank

Sand Scorpion
2p: shot deals more damage

Sonic Wings
different ships

Space Bomber
one of the secret ships is different

Strania - The Stella Machina
with two swords equipped, the mech's third swing of the swords is different

Super Space Fortress Macross
2p: faster movement

Super Space Fortress Macross II
2p: faster movement

Thunder Dragon 2
different ships

Trizeal
2p: 1) faster movement; 2) gap in laser shot is narrower

US AAF Mustang
2p: 1) lower starting rank; 2) the brown tanks in stage 8 are worth 30k each (on 1p side they give no points at all)

Varia Metal
second button is different. You either get a bomb (1p) or a shield (2p)


Thank you:
@PearlescentX, @Arasaka9, @JaimersSTG, @SPE2500, DBS, @SGP009, Ako, sikraiken, Ricardo