If you're following a Steam guide with a 3DS cart in, stop: the two versions use mostly different unlock rules. HD came out twice, in 2013 on PC, PS3, Xbox 360 and Wii U, and in 2017 on PS4 and Xbox One (August) and Switch (November). The 2017 release includes the earlier DLC and adds a second bonus stage, The Ghost Ship: Chaos. The 3DS game has 18 Raid Mode looks: 14 outfits for Jill, Chris, Parker, Keith, Jessica and Quint, plus one look each for Raymond, O'Brian, Morgan and Norman. HD keeps those 18 and adds seven more. The 3DS list comes first, then what changes in HD.

3DS outfits and the missions that unlock them
The 3DS game never names an outfit when you earn one. The Missions menu just says "New outfit" under the reward. The outfit names on this page (Diver, Beach, Snowy Mountain, Home Base, Vintage) are the Resident Evil Wiki's labels; that's a fan wiki, not Capcom. Mission names and requirements are the 3DS game's own text.
Three looks are yours from the start: Jill (Diver), Chris (Snowy Mountain) and Parker (Diver). Raid Mode itself opens through the Missions menu. Clear Episodes 1 to 3 of the campaign, then claim the Chapter 1 mission, whose reward reads "Raid Mode Stages 1 to 7 unlocked". Outfit rewards are claimed from the same menu.
| Character | Outfit (wiki name) | 3DS mission | What the mission asks |
|---|---|---|---|
| Jill Valentine | Diver | None (starting look) | - |
| Jill Valentine | Beach | Level 5 | Reach player level 5 |
| Chris Redfield | Snowy Mountain | None (starting look) | - |
| Chris Redfield | Diver | Level 30 | Reach player level 30 |
| Parker Luciani | Diver | None (starting look) | - |
| Parker Luciani | Beach | Level 20 | Reach player level 20 |
| Parker Luciani | Vintage | Legendary Weapon | Obtain a super rare weapon |
| Keith Lumley | Snowy Mountain | Chapter 2 | Clear Episodes 4 - 6 |
| Keith Lumley | Home Base | 50 Missions | Complete 50 missions |
| Jessica Sherawat | Diver | TRENCH Cleared | Clear all stages in Raid mode on TRENCH |
| Jessica Sherawat | Snowy Mountain | Level 10 | Reach player level 10 |
| Jessica Sherawat | Vintage | Level 40 | Reach player level 40 |
| Quint Cetcham | Home Base | Level 50 | Reach player level 50 |
| Quint Cetcham | Snowy Mountain | 100 Missions | Complete 100 missions |
| Raymond Vester | His only look | CHASM Cleared | Clear all stages in Raid mode on CHASM |
| Clive R. O'Brian | His only look | ABYSS Cleared | Clear all stages in Raid mode on ABYSS |
| Morgan Lansdale | His only look | Ghost Ship 100% Cleared | Find the real goal area in the ship |
| Jack Norman | His only look | Legendary Raider | Obtain all super rare weapons |
All 56 Missions menu entries, including the rewards that aren't outfits, are on the missions page. 56 is the number of entries in the menu; it isn't a cap on how many missions you can complete.
Jill Valentine

Beach is the Level 5 reward, the lowest of the level missions. On HD the same outfit needs a super rare weapon instead, so a Steam guide will send you the wrong way here.
Chris Redfield

Chris starts in the snow gear and earns Diver at level 30, the same as on HD. Leaving out the three starting looks, it's one of four outfits that unlock the same way on 3DS and HD.
Parker Luciani

Vintage comes from Legendary Weapon, which asks for one super rare weapon. The mission text, "Obtain a super rare weapon", doesn't name any. The Resident Evil Wiki lists four: Pale Rider, Drake, Muramasa and High Roller, though High Roller is disputed (more on that below). All four are on the weapons page. The 10,000-kill requirement people quote for this outfit is an HD rule; the 3DS game doesn't use it.
Keith Lumley

Keith has no starting look on 3DS; his first one comes from the campaign. Snowy Mountain is the reward for the Chapter 2 mission ("Clear Episodes 4 - 6"), which also gives "Raid Mode Stages 8 to 12 unlocked". Home Base comes from 50 Missions ("Complete 50 missions"). The game text doesn't say which missions count, but Berserker's GameFAQs guide says campaign, Raid and StreetPass missions all do.
Jessica Sherawat

Snowy Mountain and Vintage are level unlocks. Diver is the hard one on 3DS: it needs every stage cleared on TRENCH, the second of the three difficulties.
Quint Cetcham

Quint's two looks are the last main-cast unlocks on 3DS. Level 50 is the highest level mission, and 100 Missions is the highest mission count that still gives an outfit. The 200, 500 and 1000 Missions entries exist too, but they give 100000 BP, Random Weapon Lineup +1 and Random Parts Lineup +1. The 3DS game text spells his name Cetcham; the Resident Evil Wiki and most English guides use Ketcham.
Raymond, O'Brian, Morgan and Norman

All four are in the campaign story, but you can only play as them in Raid Mode. Raymond comes from clearing every stage on CHASM and O'Brian from doing the same on ABYSS. Norman comes from Legendary Raider ("Obtain all super rare weapons"). Morgan is the one that catches people out; the reason is below.
When an outfit won't unlock
The mission text for Ghost Ship 100% Cleared is "Find the real goal area in the ship", so finishing a run of the Ghost Ship bonus stage may not be enough. The wiki gives the stage objective as "Get to the deck". If the mission is still open after a clear, make sure your run ended on the deck.
High Roller is the disputed weapon. The Resident Evil Wiki counts it among the four super rare weapons and gives the same requirement for both versions. On the Trophies Hunter page for the Steam achievement, the guides say HD needs only Pale Rider, Drake and Muramasa, and several players say buying High Roller didn't trigger anything. The 3DS text never names the weapons, so it can't settle it. To be safe, aim for Pale Rider, Drake and Muramasa.
Revelations 2 (2015) is a different game with its own Raid Mode, characters and costume list, and searches for "Revelations costumes" often land on its pages. If a guide mentions Claire, Barry, Moira or Natalia, it's about Revelations 2 and none of it applies here.
The level missions use your Raid Mode player level. The wiki says any character you play raises it, though characters level at different rates. So playing as Jill still counts toward Chris's Diver outfit at level 30.
Wearing outfits in the campaign
Only HD lets you do this. HD players in a Steam discussion describe a Select Outfit option in the campaign menu once the campaign is finished, using outfits already unlocked in Raid Mode. The 3DS title menu lists NEW GAME, NEW GAME+, CONTINUE and RESTART SECTION, with no Select Outfit entry, and a GameFAQs answer says the same thing: on 3DS, outfit changes stay in Raid Mode.
On 3DS, the wiki says, a character's talents don't change when you switch outfits. In HD each outfit has its own set of abilities. The Raid Mode page has the talent list.
HD outfits: what changes from 3DS
HD adds Rachael Foley and HUNK as playable characters, plus one extra outfit each for Jill, Chris and Keith, and most of the unlock rules change. The HD rules below are the Resident Evil Wiki's. Where the 2013 and 2017 releases differ, the table gives both.
| Character | Outfit | HD unlock | On 3DS? |
|---|---|---|---|
| Jill Valentine | Diver | Starting look | Yes (starting look) |
| Jill Valentine | Beach | Obtain one super rare weapon | Yes (Level 5) |
| Jill Valentine | Pirate | Clear the Ghost Ship bonus stage | No |
| Chris Redfield | Snowy Mountain | Starting look | Yes (starting look) |
| Chris Redfield | Diver | Reach player level 30 | Yes (Level 30) |
| Chris Redfield | Sailor | Deal 100,000 damage to an enemy in one hit | No |
| Parker Luciani | Diver | Starting look | Yes (starting look) |
| Parker Luciani | Beach | Earn 10 stage bonuses | Yes (Level 20) |
| Parker Luciani | Vintage | Defeat 10,000 enemies (2013 release); 1,000 in the 2017 release | Yes (Legendary Weapon) |
| Keith Lumley | Snowy Mountain | Clear campaign Episodes 4 to 6 | Yes (Chapter 2) |
| Keith Lumley | Home Base | S rank on every CHASM stage | Yes (50 Missions) |
| Keith Lumley | Ninja | Reach player level 50 | No |
| Jessica Sherawat | Snowy Mountain | Clear every CHASM stage | Yes (Level 10) |
| Jessica Sherawat | Diver | Clear every TRENCH stage | Yes (TRENCH Cleared) |
| Jessica Sherawat | Vintage | Reach player level 40 | Yes (Level 40) |
| Quint Cetcham | Snowy Mountain | Reach player level 5 | Yes (100 Missions) |
| Quint Cetcham | Home Base | Obtain all super rare weapons (sources disagree on whether High Roller counts) | Yes (Level 50) |
| Raymond Vester | Only look | Reach player level 10 | Yes (CHASM Cleared) |
| Clive R. O'Brian | Only look | Reach player level 20 | Yes (ABYSS Cleared) |
| Morgan Lansdale | Only look | S rank on every TRENCH stage | Yes (Ghost Ship 100% Cleared) |
| Jack Norman | Only look | Clear every ABYSS stage | Yes (Legendary Raider) |
| Rachael Foley | Diver | Earn your first Trinity Bonus | No |
| Rachael Foley | Ooze | Paid DLC in 2013. Included in the 2017 release, where the wiki lists "Acquire 100 bonuses" for Switch | No |
| HUNK | Default | S rank on every ABYSS stage | No |
| HUNK | Lady HUNK | Paid DLC in 2013. Included in the 2017 release, where the wiki lists "Acquire 150 bonuses" for Switch | No |
The 3DS results screen names four stage bonuses: Perfect Shot, Genocide, No Damage and Trinity. Per the wiki, Perfect Shot is 100% accuracy and only exists on 3DS; HD swaps it for Low-level (your level is at or under the stage's recommended level). Genocide is every enemy killed, not counting Sea Creepers in the water. No Damage means you took no hits. Trinity is all three on one run, and Rachael's HD Diver outfit needs your first Trinity Bonus.
On HD the two weapon missions are awards: Legendary Find ("Obtain a super rare weapon.") and Legends Are Made, Not Born ("Obtain all super rare weapons."). There they give Jill's Beach and Quint's Home Base. On 3DS the matching missions give Parker's Vintage and Norman.
Quick lists by version
Outfits in both versions (18)
Jill: Diver, Beach. Chris: Snowy Mountain, Diver. Parker: Diver, Beach, Vintage. Keith: Snowy Mountain, Home Base. Jessica: Diver, Snowy Mountain, Vintage. Quint: Home Base, Snowy Mountain. Raymond, O'Brian, Morgan and Norman: one look each.
HD only (7)
Jill: Pirate. Chris: Sailor. Keith: Ninja. Rachael: Diver, Ooze (DLC). HUNK: Default, Lady HUNK (DLC).
Same unlock on 3DS and HD (4, not counting starting looks)
Chris Diver (player level 30), Keith Snowy Mountain (campaign Episodes 4 to 6), Jessica Diver (every TRENCH stage) and Jessica Vintage (player level 40). The three starting looks are the same too. The other 11 shared outfits unlock a different way on each version.