Sorry to be late to the party. I'm way behind on my forum reading. In answer to the original question from @brew_cat, I've spent a fair amount of time in Germany where I have often seen a bartender stir a beer with something like a coffee stir stick to whip up a foamy head.
As for CO2, Nitrogen and Beer Gas: A key point here is that CO2 dissolves in most liquids while Nitrogen does not. That's why CO2 pressurized beer is nice and bubbly (carbonated) while Nitrogen pressurized wine is not - thank goodness.
We are lucky that the CO2 pressures which carbonate our beer to enjoyable levels also happen to be about the right pressure to dispense the beer through reasonable lengths of small diameter line. The somewhat lower carbonation levels typical of porters and stouts tend to not generate much of a frothy head however. To generate the thick creamy froth of the classic "perfect pint of Guinness", we need more pressure and a stout faucet which includes a restrictor plate. Turning up the CO2 pressure results in over-carbonated beer however. That's where beer gas comes in. With 75% Nitrogen and 25% CO2 you can dispense at higher pressures with only about 1/4 of the pressure contributing to carbonation of the beer. Some bars and restaurants, with keg rooms a distance from the taps, use beer gas so they can set higher pressures to overcome the resistance of long beer lines without over-carbonating the beer. (Larger diameter beer lines may be a better solution.)
As @hd4mark pointed out, beer gas is typically dispensed in Nitrogen tanks, and with Nitrogen regulators, which are designed for higher pressures than CO2 equipment.
Most of the gases we use (like CO2 and Propane) are actually in liquid form in the tank, with some gas on top, at least until the tank is nearly empty. The gas pressure in the tank, and on the high pressure side of the regulator, is a function of the kind of gas and its temperature. (That's why the high pressure gauge on the regulator doesn't really tell us how much gas is left. The pressure only begins to drop when the tank is nearly empty.)
At room temperature, the pressure in a tank of Nitrogen will be higher than the pressure in a tank of CO2. The tanks, valves, regulators are designed accordingly. Mixed gas in a CO2 tank could over-pressurize things, which is obviously dangerous, so Nitrogen equipment is used.
If you want to dispense both stout from a stout faucet and other beers for a traditional faucet, you probably want two separate gas sources, one beer gas and one pure CO2. You may also want multiple regulators off the CO2 source, to vary pressure by beer style.