He's banned in mono as well. All OU restrictions also apply to Mono with the addition of aegislash on Steel teams.
Here ya go, champ. All the info you need.
And just to clarify on that tier clause for OU
Final edit: I was informed that the brick and mortar packet data is incorrect, and that the clause regarding OU clause exclusions only applies to move restrictions and similar. Uber restrictions on OU no longer apply, and the monotype will soon be broken up into tiers of its own.
Final answer: Landorus is not banned in Monotype because the council is relatively new and has had to give priority to too many flying type suspects already. When monotype is broken into tiers (monotype uber, ou, uu, etc...) later this year with LC, the restricted lists will be fleshed out.
Big argument was why Blaziken was banned but Landorus T was not, as they use a three type rule. If a Pokemon can create an 80 percent win rate or higher against 3 or more types on its own, it meets the criteria for ban. Landorus T fits the bill.
Give it time and the format will adapt.