I'm using an iPad Air 2. I just got the game and no enemies appear. I can only kill enemies by counter attacking or guessing where a enemy is standing. When they attack me I just see - hp and - hp again if I counter attack, once a enemy dies I see some guts on the floor. I beat the first level and tried second level and had some problem. I then turned the iPad off and back on with no change. I then deleted the game and reinstalled it, again no help. It is not plausible to play a game against invisible enemies.
@skimanner - sorry that you've hit this bug. It is in v2.3.1 and is effecting some iOS devices. We have already fixed the bug with v2.3.3 which is currently in review with Apple. Hopefully, that release will be posted early next week. Until Apple finishes its review cycle on the game, we are sorry, but there is nothing we can do. We agree, the game cannot be played against invisible enemies.
Sorry this slipped through our testing -- all of our standard test devices (multiple iPads and iPhones) did not exhibit the bug. We were able to borrow an iPhone 6s which had the issue and fix it.