Just like the previous comment from CatalinaTiger says, the 500 achievement for altars gives a +4x, or as Taiga said, a 5x multiplier (10). The 400 achievement gives a +3x, or 4x multiplier (8). This would mean the 100 achievement would give a +0x, or 1x multiplier (2). The same may be true for barracks, arena, and castle multipliers.
If the 100 achievements for the barracks, arena, castle, and altar boost the multiplier to 1, is there no gain from those buildings before the achievements, or do those achievements do nothing?
Nice. There was a glitch, though. On one stage my mouse froze (?). You should fix that (If it was meant to do that, then sorry for bugging you). If it is a glitch, and happens to anyone else, all you have to do is right click, then click on the game screen. Then you can see your regular mouse.
Anyway, GREAT game. 5/5