In regards to card type, I feel like all of the League Champions should be restricted to either Normal, Effect or Ritual cards. Rituals get a pass due to the lore behind Fiddlesticks, Nocturne and Illaoi. However, there should still be bonuses for creating extra cards that tie in with said champions.
This means no Fusions (exceptions if they're done thematically), XYZ, Synchros, Tuners, Pendulums or Link monsters. No Spell Cards (except rituals for summoning specific champions or tying into their abilities/mechanics). And no Trap Cards (except for tying into Champion ability mechanics).

Miss Fortune, the Bounty Hunter
Fire
6 stars
2400 ATK/1000 DEF
Warrior/Effect
If this card destroys a monster as a result of battle, inflict direct damage to your opponent equal to the level of the destroyed monster x 300.
EXO Shell
Equip Spell
Equip only to a "Miss Fortune" monster. Once per turn, the equipped monster cannot be destroyed by battle. You can banish this card from the graveyard; all Gun Goddess monsters you control are unaffected by card effects until the end of the turn.
Gun Goddess - Scarlet Fair
Earth
8 stars
3200 ATK/2000 DEF
Machine/Fusion/Effect
You can special summon this card from the Extra Deck by banishing 1 "Miss Fortune" monster you control equipped with "EXO Shell" OR by returning one Gun Goddess monster you control to the extra deck, and this card cannot be summoned by any other method. When this card is special summoned, you may add to your hand one card from your deck that specifically lists "Miss Fortune" in its card text. This effect can only be activated once per turn. During your battle phase, you may play any normal spell cards from your hand as if they were a quick play spell.
(This card is always treated as a "Miss Fortune" monster.)
Gun Goddess - Zero Hour
Dark
8 stars
3200 ATK/2000 DEF
Machine/Fusion/Effect
You can special summon this card from the Extra Deck by banishing 1 "Miss Fortune" monster you control equipped with "EXO Shell" OR by returning one Gun Goddess monster you control to the extra deck, and this card cannot be summoned by any other method. This card's battle position cannot be changed or forced by card effects. This card inflicts piercing battle damage. Monsters this card destroys in battle are banished instead of being sent to the graveyard and must remain banished (even if this card leaves the field or has its effect negated).
(This card is always treated as a "Miss Fortune" monster.)
Gun Goddess - Royal Arms
Light
8 stars
3200 ATK/2000 DEF
Machine/Fusion/Effect
You can special summon this card from the Extra Deck by banishing 1 "Miss Fortune" monster you control equipped with "EXO Shell" OR by returning one Gun Goddess monster you control to the extra deck, and this card cannot be summoned by any other method. This card can attack all monsters your opponent controls, once each. Your opponent cannot summon monsters during either player's battle phase.
(This card is always treated as a "Miss Fortune" monster.)
Gun Goddess - Starswarm
Fire
8 stars
3200 ATK/2000 DEF
Machine/Fusion/Effect
You can special summon this card from the Extra Deck by banishing 1 "Miss Fortune" monster you control equipped with "EXO Shell" OR by returning one Gun Goddess monster you control to the extra deck, and this card cannot be summoned by any other method. During the battle phase, your opponent cannot activate set Spell/Trap cards. Once per turn, you can destroy all face-up Spell/Trap cards your opponent controls. You cannot conduct your battle phase if you activate this effect.
(This card is always treated as a "Miss Fortune" monster.)
I happen to love MF's Gun Goddess skin, so I wanted to play into its ability to switch between suits and allow her arsenal to determine her effects. You may notice that her attribute changes between the fusions as well based on her weapon arsenal. You can find the lore details here.