This is a complex idea, but that could be awesome... to a certain extent. So, you pick your champ, but THEN you pick a passive from the champions you could have picked (including the one you actually picked) then 3 basic spells (does not need to strictly be a Q, a W, and an E: can be a Q - E - Q or a W - E - E) then an ultimate.

There would be some restrictions, though (remember: it is not meant to be balanced!)

General
  • Melee champions are considered ranged when their range exceed 350 due to abilities like Draw a Bead Draw a Bead or Massacre Massacre.
AatroxSquare Aatrox
  • If picked, you can only choose spell that either cost health or nothing.
  • Blood Well Blood Well
    • Blood Well is displayed as a buff.
AkaliSquare Akali
  • If picked, you can only choose spell that either cost energy, health or nothing.
  • Mark of the Assassin Mark of the Assassin
    • Cost and replenish mana if picked with a champion that uses mana.
  • Twilight Shroud Twilight Shroud
    • Cost mana if picked with a champion that uses mana.
  • Crescent Slash Crescent Slash
BrandSquare Brand
BraumSquare Braum
CassiopeiaSquare Cassiopeia
DariusSquare Darius
DianaSquare Diana
Dr. MundoSquare Dr. Mundo
  • If picked, you can only choose spell that either cost health or nothing.
EliseSquare Elise
GarenSquare Garen
  • If picked, you can only choose spell that either cost health or nothing.
GnarSquare Gnar
  • If picked, you can only choose spell that either cost health or nothing.
  • Gnar has no secondary bar.
  • Gnar has 150 melee range by default.
  • Gnar MegaSquare Mega Gnar spells cannot be directly picked.
  • Rage Gene Rage Gene
  • GNAR! GNAR!
HeimerdingerSquare Heimerdinger
Jarvan IVSquare Jarvan IV
JayceSquare Jayce
KarmaSquare Karma
KarthusSquare Karthus
  • Death Defied Death Defied
    • Movement abilities cannot be used during its duration.
KatarinaSquare Katarina
  • If picked, you can only choose spell that either cost health or nothing.
KayleSquare Kayle
  • Righteous Fury Righteous Fury
    • Increases attack range by 400 (still 525 for KayleSquare Kayle or any other 125 range champion).
    • Melee champions are considered ranged while under its effects.
KennenSquare Kennen
Kha'ZixSquare Kha'Zix

LeBlancSquare LeBlanc

  • Mimic Mimic
    • Works with any ability.

Lee SinSquare Lee Sin

  • If picked, you can only choose spell that either cost energy, health or nothing.
  • Flurry Flurry
    • Replenish mana if picked with a champion that uses mana.
  • Sonic Wave Sonic Wave / Resonating Strike Resonating Strike
    • Cost mana if picked with a champion that uses mana.
  • Safeguard Safeguard / Iron Will Iron Will
    • Cost mana if picked with a champion that uses mana.
  • Tempest Tempest / Cripple Cripple
    • Cost mana if picked with a champion that uses mana.
    • Cripple Cripple also benefits from an ally's Tempest Tempest.
LuluSquare Lulu
LuxSquare Lux
MordekaiserSquare Mordekaiser
  • If picked, you can only choose spell that either cost health or nothing.
  • Iron Man Iron Man
    • Shield is displayed as a buff.
NidaleeSquare Nidalee
OriannaSquare Orianna
PantheonSquare Pantheon
QuinnSquare Quinn
RenektonSquare Renekton
  • If picked, you can only choose spell that either cost health or nothing.
  • Renekton has no secondary bar.
  • Reign of Anger Reign of Anger
    • This spell cannot be picked.
  • Cull the Meek Cull the Meek
    • Cannot be empowered.
  • Ruthless Predator Ruthless Predator
    • Cannot be empowered.
  • Dice Dice
    • Cannot be empowered.
  • Dominus Dominus
    • Doesn't generate fury.
RengarSquare Rengar
RivenSquare Riven
  • If picked, you can only choose spell that either cost health or nothing.
RumbleSquare Rumble
ShenSquare Shen
  • If picked, you can only choose spell that either cost energy, health or nothing.
  • Ki Strike Ki Strike
    • Replenish mana if picked with a champion that uses mana.
  • Vorpal Blade Vorpal Blade
    • Cost mana if picked with a champion that uses mana.
  • Feint Feint
    • Cost mana if picked with a champion that uses mana.
    • Does not lower the cooldown of Ki Strike Ki Strike if you haven't picked it.
  • Shadow Dash Shadow Dash
    • Cost and replenish mana if picked with a champion that uses mana.
ShyvanaSquare Shyvana
SkarnerSquare Skarner
SonaSquare Sona
SyndraSquare Syndra
ThreshSquare Thresh
TristanaSquare Tristana
  • Explosive Shot Explosive Shot
    • Range is Current Attack Range + 100, with a minimum of 650.
TryndamereSquare Tryndamere
  • If picked, you can only choose spell that either cost health or nothing.
  • Tryndamere has no secondary bar.
  • Battle Fury Battle Fury
    • This spell cannot be picked.
  • Bloodlust Bloodlust
    • Does not consume fury, and only heals for the base amount.
  • Undying Rage Undying Rage
    • Does not grant fury.
TwitchSquare Twitch
UdyrSquare Udyr
UrgotSquare Urgot
VayneSquare Vayne
Vel'KozSquare Vel'Koz
ViktorSquare Viktor
VladimirSquare Vladimir
  • If picked, you can only choose spell that either cost health or nothing.
WarwickSquare Warwick
Xin ZhaoSquare Xin Zhao
YasuoSquare Yasuo
  • If picked, you can only choose spell that either cost energy, health, or nothing.
  • Way of the Wanderer Way of the Wanderer
    • Flow is created as a buff.
ZacSquare Zac
  • If picked, you can only choose spell that either cost health or nothing.
ZedSquare Zed
ZyraSquare Zyra

So, what do you think about it?

  • P. S.: It took me more than an hour to do the entire restriction list.
  • EDIT: Here is the inspiration.
  • EDIT 2: Any one who played Dota 2 recently probably knows the Ability Draft game mode. Well, it's kinda like this one (you have a random hero instead of pick, and the spell pool is the one of the 10 heroes picked + 2)