One of the 4 factions, Human creatures are normally portrayed as angels, knights, and royalty. They are "strong" against the Mortii faction, and "weak" against the Neander faction. Their ability, Consecrate, increases their ATK when attacking a Mortii creature.
Human creatures are notorious for buffing each other with their Humanity and Sage Advice abilities. Also, due to Human 3 and 4 star heroes having Ice Shell, they will be pretty tanky during the first 10 or so turns of a battle. Humans also like to heal and use Restoration a lot, so abilities like Rip and Delay are recommended when going against them.
The Sacrifice 8 Graboid, one of the most popular melded creatures, is a Human deck's worst enemy. If your creatures aren't melded with Frost Armor, then a Sacrifice 8 Graboid will easily deal over 4,000 damage to 3 of your creatures at a time. Also, due to how tanky Human creatures can be, people tend to use Wight against Human decks. In order to counter this, one must use a Warlock in order to get rid of Wight's Death Curse.