What...? Exo can use smasher as many times as they want. Slow heal as well.
There is no limit to how many times you can use skills, but some of the higher end skills require clear cube PIECES. Usually lv35 skills and up.
You also need the MP for it as well and MP recovery items don't come cheap. Cheaper than HP but still expensive. Learn to conserve your MP whilst finishing the dungeon.
You've been warned.
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Beatmania IIDX ftw! 
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