Marris Otter is very high modified malt and enzymes need to be added to make ale and lager with it. Marris Otter was originally intended to make whiskey with. The malt contains Alpha, saccharification will occur, but conversion won't because Beta is wiped out. The complex sugar required in ale and lager, maltose and maltotriose, will not form. Enzymes are manufactured to make up for deficiencies in malt.
A spec sheet comes with each bag of malt and it is used to determine if the malt is good to make ale and lager with or if it is more suitable for making whiskey with. Extract efficiency, gravity per pound, pH, color, modification level, percentage of protein are a few things listed on a spec sheet.
When a recipe recommends high modified malt, single infusion, no Beta rest, no secondary fermentation, and priming the beer with sugar or injecting the beer with CO2 for carbonation, the beer will be similar to Prohibition style beer.
Check out the recipes on Weyermann Malt website.
Weyermann Pils dark floor malt and some sauer malz is all that's needed in Oktoberfest, along with step mashing. Decoction method would be better because when mash is boiled a type of heat resistant, complex starch called amylo-pectin enters into solution. During dextrinization Alpha releases A and B limit dextrin from the starch which are tasteless, nonfermenting types of sugar responsible for body and mouthfeel. The decoction method produces clean, chemical, sugar and nutrient balanced wort less likely to develop the off flavors associated with single infusion brewed beer.
I use Weyermann dark and light floor malt for making Ale, Lager and Pils with the tri-decoction brewing method. The malt is slightly under modified and low in protein. Under modified malt is rich in enzyme content and low protein means it is rich in sugar.
