Very interesting question ! So many possibilities ...
I think about the Scourge of Corruptor + the Wasp Gun = the Persecutor : lots of tiny homing eaters ! Perfect to eat ennemies alive ! It deals magic damage and have no mana cost, because of the SOC's priceless nature.
Then, we got the Venom Staff + the Razorpine = the Poisoned Nightmare : spread a deadly plague with a consequent rain of painfull needles ! Insane rate of fire, amazing DPS with a great poison effect, but huge mana cost.
And why not this one, Heat Ray + Sniper Rifle = the Shockwave Rifle : an extremely powerfull sniper who shots a deadly ray of pure concentrated energy. This laser is able to pierce up to 10 ennemies and bounce 3 times. The fire rate is greatly increased compared to the Sniper Rifle's one.
We can imagine the Stynger + the Blizzard Staff = the Eleventh Plague : bring the desolation with a rain of explosives stinger-bolts. Each one realeases 3 shrapnels upon exploding! Say goodbye to your computer ...