One of the biggest changes in Pokemon Go's new update is the addition of a new "motivation" mechanic. Every Pokemon stationed at a gym has a motivation stat equal to their CP, which goes down over time. In addition to natural attrition, motivation will also decrease in large chunks whenever a Pokemon loses a gym battle.
Pokemon Go players are still trying to understand how motivation works, but one fact has become painfully obvious. Pokemon with high CP seem to lose motivation a lot quicker than other gym defenders.
Players have discovered that Pokemon with a CP of 3,000 or higher lose motivation at a significantly higher rate. It seems that a 3,000 CP Pokemon loses about 10% of its maximum CP per hour, while all other Pokemon lose only about 1% of its maximum CP per hour.
The rate of decay is pretty obvious when you look at any high level gym. Pokemon like Blissey, Dragonite, and Tyranitar typically have some of their motivation lowered, while all other Pokemon are seemingly unaffected by motivation loss.
There's a couple of theories as to why Pokemon Go is punishing players for having high level gym defenders. The most obvious possibility is competitive balance. Battling a Blissey at full strength sucks, even for high level players, but the CP decay seemingly helps even the odds.
It's also possible this is some sort of weird glitch...which wouldn't exactly be surprising given Pokemon Go's past track record.
Whatever the reason, players who want to use a Dragonite, Blissey, Tyranitar, or another high CP Pokemon in battle better have a steady stream of berries ready to use. Otherwise, their Pokemon could quickly be given the boot the next time their gym comes under attack.
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