I want to know how these interact with Gazlowe. If something's cost is reduced to 1 do I still get the mech? The main card I want this to work with is Summoning Portal, but interested in the others as well.
Remember he doesn't work with minions - only spells - so summoning portal would never work for instance. I believe an unstable portal at a minus-1 mana cost (assuming Thaurrissan or Sorcerer's Apprentice) would trigger him.
Yes; Gazlowe's effect triggers off what you pay, meaning if a spell is reduced to 1-mana you will get a mech from Gazlowe. Keep in mind Gazlowe's effect only triggers off of spells though, meaning Summoning Portal won't really interact with him (barring making it easier to play the cards you get).