User blog comment:Iyreguy/Unofficial Tournament!/@comment-3153244-20120707132249/@comment-5087069-20120707175348

It allows the player to truly help wim with the build. Now the reason why specialty buildings are allowed and not premiums and special agents, the factors are:

NK Coins (That plays a huge role in BTD5 and must be purchased by real money. In addition, the premiums purchased by it give real huge buffs, even more than Special Agent Pros do. Some people might not be willing to play with real money, so we will respect that. Keep that in mond.

Power: You are allowed to have at most 1 Specialy building on at a time, but unlimited special agents. Most of these special agents can also pop lead, see camo, and destroy multiple layers. Assuming most of you (if not all) have Special Agent Pros, which are really deadly. Some people might not have enough MM for all that stuff, and it is enugh pain to get it through special missions. Special agents can really mess up the chance of having a 'fair game'.

Buffs and debuffs: Think about it. How many Premiums/Agents buff something? All of them, at least. Now how many of them buff AND debuff something at the same time. None of them, of course (If we dont count the part where you cant put water towers on pontoons and land towers on Portable lakes, but that is minor as you can sell them (for $0 though). Now every specialty building goes like this:

Level 1: Reduces Cost of tower and its upgrades.

Level 2: Usually increases attack speed of tower

Level 3: some kind of special thing about the tower (ex. Super Monkeys can detect Camo or the Shadow Double Ability for Ninja Monkey)

However, increases the cost of another tower and it's upgrades.

Assuming that all of you should have at least 1 lvl 1 or higher Building.

Now the main reason I allow them is in its name: Specialty. Say you might be good at using a certain tower. You specialize in that tower, using it to your advantage, while making something else harder to succeed with.

Get the point now?