I ran some tests. The 2 creeping melee dmg debuff pets, 1 single target ranged (spore cannon?) And the pbaoe one (sporespawn?) Do not impact the damage of players. This was tested in a duel with a hero using speer weapons, both fully buffed. It didnt lower the heros damage vs the animist or shroom. It is suppose to reduce damage by around 15% depending on which level of shroom.