Not really a bad idea. However, if players have been given a “taste” of what that new hero can do in maps, people will get very much disappointed dumping money just to have an abysmal odds of getting such hero with nothing to show for the money spent. Or that players already knew the odds that its much better to get them thru regular portals using free pulls than chasing them after swearing not to spend another dime on the game just because they are so good.
I think that idea might create an avalanche of complains like this
“When I tried this hero which has 33% chance of missing, this hero never missed a hit. Now that I own this hero, misses every attack! What a scam!”
Basically complains about any feature (accuracy or whatever other you may think) that people thought was cool when they tried it but turned out not to be so cool in their point of view when they actually summoned the hero.
Not a good idea, because you are putting a beta hero is the arms of the general public, and opening up a big can of worms. You want to be a beta tester, then apply as one.
So basically it would be a story thing where, for example, Dr Moreau says “On this stage/province, I will help you” and then he occupies one of the spots in your team and you fill the 4 other spots with your own heroes.
Players were given sort of a taste of this during the tutorials, when you were able to play a few preset stages with Colen, Lianna, and Commander Grey (who for some reason remained outside of the available hero roster), until reality sets in, the actual game begins, and you are given Sharan, Derric, Brand and Bane.
Come to think of it, there is really no reason why Commander Grey shouldn’t be made an acquirable hero, now that the Dark Lord is also attainable.