Each Fungus creature gets +1/+1 for each spore counter on it.
{B}{G}, Exile a Fungus card from a graveyard: Put a spore counter on each Fungus on the battlefield.
Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to a Fungus creature may become lethal if Thelon leaves the battlefield during that turn or if spore counters are removed from the Fungus during that turn.