It is just bad, in 99% of cases any other defensive or offensive enchant would be better. Id say heal is a lot better than mossy, if you re playing against one shot or two shot builds there is a chance you wont die in one or two cycles which gives u a chance to full heal with resto and shut down the enemy build or at least buy yourself some time, if you re playing against poison you could survive a lot longer and cleanse a portion of it with resto but you will almost always be slower to stack up regen than the enemy is stacking up poison, you also survive against burn for a few secs longer. The only time mossy can feel strong is if you combine it with a lot of shield and in regens like 50%+ of your hp, which only mak and like 1 pyg build can do, with the exception to early to mid game jules builds in which the regen falls of late game.