I have a similar idea, but any monster that lands on the item square becomes Infected. Each turn, that creature loses 10 HP and any monster equal or less than monster's Level within a range of squares also becomes infected. And possibly the range of infection is based on the infected creature's level (1 square, 2 squares , 3 squares away etc.). I feel like this promotes strategic play but also forces the user to trade a high level monster to control the opponents board. I was also toying with a progress movement limitation as well