And also, as for Costumes I would like............. this list may be a bit odd, but hey, you asked for my personal opinion, so that I shall give you-
(And also I know you asked for Gunner specifically, but I will broaden my list to all 3 Mii Fighters)
Blue/Red King (Clash Royale, Brawler (Shot Put makes for a great "King Tower Canonball))
P.E.K.K.A./Mini P.E.K.K.A. (Clash Royale, Mii Swordsfighter)
Knight (Clash Royale, Swordsfighter)
Archers (Clash Royale, Gunner)
Hunter (Clash Royale, Gunner)
Would be extremely cursed but, Koopa Troopa
Another Cursed one but, NES Mario Sprite
Pearl and Marina (Splatoon 2)
(The Splatoon series' shop owner characters that I can't recall the names of, and also the Jellyfish-like people found in the Splatoon Series)
Would hate to see instead of a Playable character, like many of the costumes I've already listed but, Octoling (Splatoon Series(Good/Bad))
Various Wario Ware characters I'm too lazy to list off (Already got an Ashley costume for Swordsfighter, unfortunately)
Dracula (Castlevania)
Ganon (The Legend of Zelda)
DarkNut (The legend of Zelda, Swordsfighter)
BOOOSHIIIIII (Yoshi)
Witch (Clash Royale, Swordsfighter)
Wizard (Clash Royale, Gunner)
Princess (Clash Royale, Gunner)
Medusa (Kid Icarus)
Tron Bonne (Mega Man Series)
Servbot (Mega Man Series)
Mega Man, and other Versions of Mega Man (Mega Man (obviously), Gunner)
Toadette, if not already in (Super Mario, Brawler)
Jacket and Blue Jeans- If jacket is open, make the shirt white
KoF Character costumes, such as Geese Howard
Bandit (Clash Royale, Swordsfighter)
Lumberjack (Clash Royale, Swordsfighter)
More cursed ones- Skeleton (Clash Royale, Swordsfighter), Goblin (Clash Royale), Spear Goblin (Clash Royale, Gunner)
Now things are getting stupid:
Gill Grunt (Skylanders, Gunner)
Trigger Happy (Skylanders, Gunner)
Chop Chop (Skylanders, Swordsfighter), Terrafin (Skylanders, Brawler)
Ignitor (Skylanders, Swordsfighter)
Flameslinger (Skylanders, Gunner)
Hex (Skylanders, Gunner)
Voodood (Skylanders, Swordsfighter)
Wham-Shell (Skylanders, Swordsfighter)
Zook (Skylanders, Gunner)
Water Zombie (Minecraft, Brawler)
Witch (Minecraft, Guner)
Leather, Chainmail, Iron, and Gold armor and sword (Minecraft)
Builder Outfit (Super Mario Maker Series, Brawler??)
Cut Man (Mega Man, Gunner)
Guts Man (Mega Man)
Elec Man (Mega Man)
Fire Man (Mega Man)
Bomb Man (Mega Man)
Ice Man (Mega Man)
(CUSRED) Yellow Devil (Mega Man)
And Dr. Wily! (Mega Man) (Not enough Mega Man characters???)