The hitlag multiplier's application to projectiles changes the theorycraft. This hurts these projectiles:
Falco Blaster #1 (0.1x)
Fox Blaster #2 (0.3x)
G&W Chef #3 (0.5x/0.1x/0.0x)
Greninja charged Shuriken #1 repeating hits (0.6x)
Bowser Fire Roar (0.5x)
Bowser Jr. Up-b 2 initial hit on group or aerial sourspot (0.5x)
Bowser Jr. Up-b 3 explosion (0.8x)
Link Arrow #1/3 (0.8x)
Charizard Fire Breath #1 (0.5x)
Luigi Fireball late hit (0.5x)
Luigi Iceball (0.8x)
Mario Fireball/Doc Capsule (0.3x)
Mario Fast Fireball/Doc Fast Capsule (0.0x)
Mii Gunner Grenade (0.3x repeating hits, 0.6x final hit)
Villager dash attack (0.6x)
Pac-Man Meteor Trampoline projectile hitbox (0.8x)
Pikachu Thunderwave (0.45x total)
Pikachu Thunder #1/3 initial hit (0.0x total)
Robin Arcfire #1/2/3 repeating hits + #1/2 final hit (0.5x)
Mega Man uair (0.2x)
Mega Man f-smash (0.3x)
Mega Man Crash Bomber explosion (0.3x)
Mega Man side-b #3 initial hit (0.7x)
Mega Man Leaf Shield #1/3 shield hits (0.5x)
Mega Man Leaf Shield #1/2/3 thrown hit (0.3x)
Mega Man Tornado Hold (0.8x/0.3x)
Rosalina Shooting Star Bit (0.2x)
Luma fair (0.3x)
Luma uair, late utilt, star bits #1 (0.5x)
Samus Bomb #1/3 initial hitbox (0.6x)
Samus Bomb #1/2 explosion (0.3x)
Samus Bomb #3 explosion (0.5x)
Sheik Needle Storm (0.8x)
ZSS Paralyzer #3 initial hits (0.6x total)
Toon Link Boomerang #2 initial hit (0.5x)
Toon Link Boomerang #3 (0.8x)
Toon Link Arrow #2/3 (0.5x)
WFT Hula Hoops #1 (0.0x)
WFT Hula Hoops #3 initial hits (0.5x)
WFT Condensed Sun Salutation uncharged (0.8x)
WFT Sweeping Sun Salutation (0.8x)
Yoshi up-b #1/3 hit (0.3x)
Yoshi up-b #1 explosion (0.3x)
...and helps these: (Grey attacks don't actually have a difference due to the way things are calculated)
DDD Gordo #1/2/3 (1.5x)
DHD Discus #1/2/3 hit (2.0x)
DHD Discus #1/3 shots (2.0x)
DHD Discus #3 explode (2.0x)
DHD ZZS Shot (1.2x)
DHD Gunmen #1/2 (1.5x)
DHD Gunmen #3 (2.0x)
Fox Blaster #3 (1.2x)
G&W Chef #2 (1.8x/1.5x)
Greninja uncharged Shuriken #3 (1.5x)
Greninja charged Shuriken #1 final hit (1.5x)
Bowser Jr. Up-b 2 aerial sweetspot (2.0x)
Link Arrow #2 (1.7x)
Charizard Flare Blitz explosion (1.5x)
Charizard Blast Burn explosion (2.0x)
Lucas PK Thunder (1.5x total)
Mario Scalding FLUDD (1.2x)
Mii Brawler Iron Ball (1.5x)
Mii Gunner Flame Pillar final hit (1.5x)
Mii Gunner Charge Shot max charge (1.05x total)
Mii Gunner f-smash final hit (2.0x)
Villager Explosive Ballon Trip (2.0x) --- remember, these hitboxes were significantly nerfed in size this patch!
Villager Giant Timber tree fall (2.0x)
Pac-Man default hydrant fall and hydrant projectile (1.5x)
Pac-Man On-Fire Hydrant flame initial hit (1.2x)
Pikachu Thunder Wave (2.5x/2.1x/1.5x)
Pikachu Thundershock (1.5x total)
Pikachu Thunder #1/3 later hits (1.5x total)
Olimar Explosive Pikmin Pluck (1.5x)
Robin Elwind #3 initial hit (2.0x)
Robin Arcfire #3 final hit (2.0x)
Robin (El)Thunder (1.5x total)
Robin (El)Thunder+ (2.25x total)
Robin Speed (El)Thunder (1.2x total)
Robin Arcthunder(+) (1.5x/0.6x/3.0x total)
Robin Speed Arcthunder (1.5x/0.6x/2.25x total)
Robin (Speed) Thoron(+) (1.5x total)
ROB max charge beam #1/2/3 (1.3x)
Luma Jabs 1/2/3, dash attack, bair, dair, dtilt, usmash, dsmash (1.5x)
Luma nair, fsmash (1.7x)
Luma Jab finisher, initial utilt (2.0x)
Ryu blue Hadoken (1.4x)
Ryu red Hadoken (0.25x/1.8x)
Samus Charge Shot #1/2/3 sub-max charge (1.5x total)
Samus Charge Shot #1/2 max charge (1.05x total)
Samus Charge Shot #3 max charge (3.3x total)
Sheik Penetrating Needles (1.1x) --- remember, these got a shield damage nerf
Sheik Paralyzing Needle (2.0x)
ZSS Paralyzer #1 (2.0x)
ZSS Paralyzer #2 charged (1.2x total)
ZSS Paralyzer #3 final hit (1.4x)
Toon Link Boomerang #2 late hit (1.2x)
Wario Bike #3 (1.2x)
WFT Jumbo Hoops (1.5x)
WFT Condensed Sun Salutation charged (1.5x)
Yoshi down-b 2 star (1.5x)
Yoshi up-b #3 explosion (1.5x)
Zelda Phantom #1/2/3 max charge 2nd hit (1.2x)