So I thought up a story.

A gap has opened up between the worlds of the living and the dead and a group of past villains from KR and SS have invaded the living world.

The Rangers (after much discussion with other toku fans):
Hime Shinkenred
Magiblue
Goseiyellow
Black Condor
DragonRanger
Big One
Dekamaster
MegaPink
Go-On Gold
Gokai Silver

The Riders:
#1
Stronger
Black RX
(AR) Kuuga
Decade
Fourze

The extra heroes:
Signalman
Riderman
(AR) Kamen Rider Kivala
Kamen Rider Diend
Rio
Black Knight/Kurokishi
Kamen Rider Den-O Sword Form (Momotaros)
Gavan

The villains:
Agent Abrera (Dekaranger)
Garagaranda (Kamen Rider)
Ikadevil (Kamen Rider
Doctor G (Kamen Rider V3)
Shadow Moon (Kamen Rider Black/RX)
Griffozer (Zyuranger)
Lami (Zyuranger)
Bandora (Zyuranger)
Chinomamako (Shinkener/Kamen Rider Decade)
Black Cross Fuhrer (Gorenger)
Grand Leader (Showa era Kamen Rider)
General Jark (Kamen Rider Black RX)
Akudos Gill (Gokaiger)
Apollo Geist (Kamen Rider X)
*The idea is that something happened to Bandora's dumpster to destroy it and it's contents during it's voyage in space.