MArcomage

This card, along with Dwarven wall, Wizard's Tower and maybe others that I don't remember should have an upper limit.

Check this. Angry mob, a common card, doing 34 damage!

Yeah, but you should play Gateway, Crystal cavern, Curse and Treacherous Artifact before it. It's a keywordless rare, two very expensive uncommons and +/- facility card that not so cheap with total cost of 24 bricks/154(!) gems/24 recruits. If you did that - you deserved that 34 damage from a common.

well, you can simply play Legend cards and raise your facilities while dealing damage. But it's a situational card as NG said so yeah.

The way I see it, if you (or your opponent) have cultivated such a high number of facilities, you've earned the uninhibited effect these cards can have.

Just did 69 damage with it. Two turns in a row. That was cool. :p

how does one get 23 facilities without winning or getting killed/out built?

http://arcomage.netvor.sk/?location=Replays_details&CurrentReplay=151091&PlayerView=1&Turn=1

When playing against the AI normal conventions gets blown away.

I have an old +Facilities deck that I never use, except that I did test it against the AI not long ago as well. Interesting match. This card saw some use in it, of course, but nothing quite like that.

Anything above 20 (maximum attack of Death wave) is too much for a common IMO.
And it's not so difficult to have facilities >20, especially in long mode. Gateway gives 15...