Using more than one yeast strain in one batch.

I haven't done it, but lots of people have combined two or more strains. Also, I have read (possibly in the book "Yeast" but possibly elsewhere) that in pitching the first generation of the combined culture, there's little need to worry about one strain outcompeting the other, which can happen over time in subsequent propagation of the combined culture.

 

You can ‘experiment’ and blend various yeast strains together in your homebrews.

Wyeast also makes various yeast blends:

Wyeast 3056 Bavarian Wheat Blend: “This proprietary blend of a top-fermenting neutral ale strain and a Bavarian wheat strain is a great choice when a subtle German style wheat beer is desired. The complex esters and phenolics from the wheat strain are nicely softened and balanced by the neutral ale strain.

Wyeast 2633 Oktoberfest Lager Blend: “This blend of lager strains is designed to produce a rich, malty, complex and full bodied Octoberfest style beer. It attenuates well while leaving plenty of malt character and mouthfeel. This strain is low in sulfur production.”

Wyeast 3789 (a VSS strain) Trappist Blend: “A unique blend of Belgian Saccharomyces and Brettanomyces for emulating Trappist style beer from the Florenville region in Belgium. Phenolics, mild fruitiness and complex spicy notes develop with increased fermentation temperatures. Subdued but classic Brett character.”

I have used Wyeast 2633 a couple of times to make Oktoberfest beers. It is my preferred yeast strain for this style of beer.

I have used Wyeast 3789 two times. My experience with this yeast is that it produces a very funky beer which is very similar to Green Flash Rayon Vert.

Cheers!