A pokemon that directly or indirectly limits the opponent's move options, through a combination of abilities, typings, items, etc.
The outcome of a Pokemon match depends on the skills (sometimes luck) of the trainers. Usually the one that could better predict the opponent's moves is the victor. A single mispredict can cost anybody a match. Great skills in prediction comes with experience. However, one way of increasing your chances of predicting correctly would be by limiting the options the opponent could do. If you can control the situation in such a way that he is restricted to a single option, what's there to predict? That's what this concept is all about.
Questions To Be Answered:
- How much of the metagame is susceptible to move restriction?
- To what degree can a certain Pokemon affect the options of an opponent?
- Would the opponent choose the less ideal option, knowing that the option he has been restricted to is what you chose?
- How do other Pokemon adjust their movesets and strategies with the Restrictor Pokemon around?
To better understand what I'm trying to say, take a look at this Move Restriction Guide
onsite. The article "takes a close look at the workings of moves, items, and abilities that restrict the move options available to Pokémon". There's a multitude of ways that this can be accomplished, so we don't even have to be restricted by this article. It is possible for the Concept to go for an offensive route, using its threat as a restricting factor as well. However, a more defensive approach may be better suited for it. For example, when pulled off right, a Pokemon with enough defenses to take a hit with the moveset of Spider Web / Substitute / Disable / Encore with Prankster completely restricts the opponent's option to Struggle!