I just thought of fusing weapons.Here are some things.

Callahan+polaris= Thunder Crasher
This weapon will be a callahan with a lightning fuse and shocking outer shell.
it will shoot super speed bullets that will burst.
The charge attack will back the explosion shoot out shells that make more explosion.
WARNING:LAGGGGGG

I was thinking to only alow fusing in shadow lair so these weapons won't be common.
If they both have UVs they can only add up to 3 UVs and the others will be deleted of your choice.
Another mat you can have to make this all work will be a new mat called "Fusing crystal".
Also you fuse the 4* of it not the 5*.
the materials would be callahan+polaris so alot of mats.
the recipe be like:

Thunder Crasher (Recipe)
Red shards:15
Blue shards:15
Bronze Bolts:8
Iron gears:3
Force dynamos:2
Heavy gear:1
Gremlin gizmos:3
Rocket sprocket:1
Volt oil:1
Thunderball:1
Fusing crystal:1
Kilowatt pulsar 4* lv 5
Mega magnus 4* lv 5