You need to get 100 coins total (does not have to be done in one sitting).
I can verify that your coins collected across all modes (Adventure, Survival, and Practice) are all added together and can be kept track of by the screen you get from completing a level as well as from losing all your lives and getting a game over screen. Your coins that you have total will be in parentheses and the coins you just earned this level or game will be to the left of the parentheses.
The achievement will pop at either the end of the level screen or when you lose your last life and get a game over screen.
There was some missinformation on this achievement, I hope this clears it up. I personally unlocked the achievement in Practice mode to test my theory. The first level is easy to do it on but there are many other levels that are good too.