Prohibition, What About Maindecking?

Activate by declaring 1 card name. Cards with that name, and their effects, cannot be used. Cards already on the field are not affected (including face-down cards).

Great side deck card it is, isn't it? Generic enough to be a generic side deck card against every deck. For this exact reason this card is primarly used for random decks you could encounter in a tournament but that you weren't ready for so that you didn't side anything. But, let's be a little more specific: every deck has a key card or some cards that they'd suffer alot to lose, or even cards that you don't want yourself to face. This card will always be there for you (looks romantic as a statement, doesn't it?).
So, what am I reviewing this card for? Maindeck it.
When there's a card enough specific to always be used it is considered a staple, let's say Reborn, Heavy and Dark Hole. Dark Hole and Heavy Storm are in the 90% of cases great minuses for the opponent and they could win your game, while reborn is played even in macro decks because SSing something without any cost is just great. No limit for the summon, even the opponent's grave is ok, and you can bring your opponent's BLS.
Prohibition does just the same, but even better: DH isn't good against some decks, Heavy isn't against other, Reborn suffers Macro decks, but this card can slow down ALL of them, or even kill some of them (prohibition on sea lancer is pretty much an auto-win, if you can protect prohibition).
Here's another factor, protection. Sometimes you can use Prohibition to protect yourself from DH when you overextended and opponent used fader or swift scarecrow, or even gorz. Sometimes you can use Prohibition on MST (maybe along Starlight face-down) to protect your field spell, your continuous cards, your face-downs, and your prohibition itself. Sometimes you can use prohibition when you see your opponent has 3 DARK monsters in grave on DAD.
This all makes maindecked prohibition great for lots of decks, from OTKs to control, to Antimeta, to Macro, to Skill, to Grave-reliant, to SS-reliant and so on.
Focusing a bit more on OTKs, you can use Prohibition on Gorz, Fader or Scarecrow (based on what you think opponent has in hand), or, if he has a set card, on Mirror Force, Prison or Compulsory. If you're comboeing and your opponent has a face-down, declare that Solemn Warning or Torrential Tribute right away.
Focusing on Control/Antimeta decks, stopping MST and Heavy Storms isn't everything you can do. If you play, let's say, a Control deck that focuses on bringing a boss monster to win, you can declare Solemn Warning and summon without worrying.

This is in game 1, in early game, where you don't even know what the opponent's playing, in mid and late game you can easily kill decks once you know what they're playing. Go for Prohibition on Hornet and plan to win, or use it on REDMD to stop the infamous Lightpulsar-REDMD loop, or use it on WU-Rabbit to stop some more abuses or Magician if he has yet to combo, while Mermails could lose some power once you stop their infantry, because they'd lose their raigeki break for face-ups that's searchable and abusable and that could destroy that prohibition itself. Everything suffers at least a bit Prohibition, even in game 1.

In game 2 and 3, if you didn't side out those prohibition (I'd always recommend to keep them, though, except for some rogue and such), this card gives you the upper hand since you won't have to side out anything to fit them, they're already in! Side what you want, and if it is a continuous spell/trap, declare MST.
Use this on Magician and protect it well, you should have already won like this. I won't explain all the decks cause you should know their main cards, just know that everything suffers, rogues and similar apart.

In game 2 and 3, too, you can use this card to counter-side. Basically awesome. You playing Wind-Ups? Go for Needle Ceiling. Playing Chaos Dragons? Fissure. Fear opponent's Prohibition? Prohibit it. (If you're asking if it is possible, yes it is).

Well, I described Prohibition as a meta call, sometime I should show you something else about Prohibition-
Stay Tuned, I prohibit you to stop following me (? LOL, just wanted to use prohibit someway, I like this verb a lot).