Heffalump is very tolerant of different flame chemistries and doesn't do anything weird when you reduce it.
Here, you can see that Heffalump is a little bluer than the new CiM Rapunzel, but pinker than Effetre Lavender Pastel.
Silver on top of Heffalump reminds me of what happens with silver on top of Vetrofond Seashell Swirl. The silver turns greyish but with pink and blue blushes to it that are quite attractive if you reduce and encase it. If you don't reduce and encase it, it sits on top of the bead like a brownish crust, fuming the Heffalump yellow around itself.
Reducing silver glass is interesting on top of Heffalump because you get the same yellowing that you get from plain silver, only you get it in a lot of different places. I am a little in love with the effect of the blues and purple of my reduction frit blend on that background of gently yellow-fumed lavender. I didn't get a particularly nice initial strike out of the TerraNova2 frit on top of this colour.
Heffalump has poor cohesion, and separates on top of Copper Green, Opal Yellow, and Ivory. On top of Tuxedo it thins out and looks almost transparent and milk-mustachey. When Copper Green and Tuxedo are used on top of it, it rises up around them in little halos. Copper Green separates a little on top of Heffalump, too, but it's hard to see because this colour is definitely not one of the ones that helps keep Copper Green clean. Ivory separates on top of Heffalump.
Opal Yellow, Ivory, and Peace all spread like mad on top of this colour, too.
These are the only beads I have to show so far with Heffalump. I'll come back and update this when there are more.