1) What do you want added to the game?
I want to add to the game elements of bluffing, make players more think strategically and make game more funny of course.
For example. It's simplified so don't think that's exactly as it is would be. Player 1 puts Mind Fortress in game. He is getting less damage, playing Living Images, using all advanteges that Mind Fortress is giving him. Player 2 have enough powerful creatures in deck, he may also have Sky Blitz. But in this game he is getting only pillars from his deck. But he isn't playing them. He is making Player 1 think that he is preparing creatures in hand to suddenly attack him, destroy Mind Fortress and win the game. Therefore Player 1 abandons fortress though in fact he was not in danger.
Isn't it funny?
I understand that my card isn't balanced but can't it be balanced?
2) Once you have identified the core of your suggestion then consider if a simpler version exists.
For bluffing one of the players might be able to use action, that he afraid of using because of other player’s chance to prevent it or use for his own advantage. Like one player afraid of growing Lava Destroyers because other player can play TUs. But this example is not very interesting and need two cards: TU and Lava Destroyer. My construction needs only one card and is more interesting.
One card, one action for owner and one action for opponent. In addition, players' hands should matter. There are of course simpler versions but there are no much simpler. And I don't know how this particular card can be simplified.
I could remove DR and rename card from Mind Fortress to Mind Portal or do something like this, but this wouldn't make card much simpler.
I could remove capturing creatures in mind and replace it with just damaging them, but this would make card less original.
I still think creature generation is the most suitable ability for Mind Fortress.
I could replace Living Images with simpler creature generation, like '2
: generate 5/5 Sick Mind Product'. But it wouldn't be interesting.
DR does not make sense. It is a mental fortress not a physical one. Your theme indicated that it left the user vulnerable to physical assault not protected from physical assault.
I think about Mind Fortress like about something created by mind but almost completely material. Mind Fortress can be used like gate from reality to mind, but it isn't something imaginary. It IS physical.
But I can remove DR anyway. Let Mind Fortress be not physical. No problem.
Immaterial does not make sense either. Your theme indicated the mental fortress would be vulnerable to physical assault. The concern you have with Explosion is unfounded if the card were balanced. Immaterial is overused in design as a crutch. You do not need it.
All right although there is Hope produced by mind and immaterial but protecting from physical damage.
4) I assume from your comment you are familiar with a fairly complex card game like MtG. Siege would be of appropriate complexity for such a game but the effect would have to be understandable from just the card and the online rules pdf. EtG is much less complex because it tries to appeal to a broader audience however like in MtG clarity is very important. A new player faces up against a Mind Fortress would have no idea if the should or should not siege based on that tiny description on the card.
Alternate siege mechanics might be useful instead. PC can be used to siege against a hand of Titanium Shields. Creatures siege against Bone Wall. Note the increases clarity for people not used to MtG level complexion.
Some players program calculating applications to find decks' FGei. I suppose it would not be bad if someone played with cards like Mind Fortress in deck.
I assume that if this card ever made into the game it would use some kind of hint or screen tips.
And I still think siege mechanics is not very complex. Player playing against Mind Fortress should understand just that he needs certain attack power to siege it, that's all.
Alternate siege mechanics might be useful instead. PC can be used to siege against a hand of Titanium Shields. Creatures siege against Bone Wall. Note the increases clarity for people not used to MtG level complexion.
I think adding and subtracting creatures' damage and life is simpler that siege with PC/CC interactions.
Thanks for reply, and sorry for making you write and read so much text. I'll think much about balance.