Let me try to help you.
Those heroes who boost a stat or add a kind of effect on itself or the allys.
Attack boost. Increase the attack.
Boldtusk, Kiril, C.Rigard, Tarlak, Miki
Is like attack boost but its not a limited amount. Lets say 40%. You see the stat increase by every hit you receive.
Def up / def elemental up
Increase the defensive stat
Kiril, Jean Francois, Guinerve, Dormitia.
Returns part of the damage inflicted
Elena, Sif, Boril. Ursena(return all damage and status from yellow)
All special skills are aimed to the hero with taunt.
Black knight, Queen of hearts, Shrrubear
Increase the mana generation
Are effects that are inflicted and are negative. They can be cleansed by c.rigard, rigard,c.sonya,c.caedmon, kunchen, vivica, ariel, raffael
Slow down mana generation
Mist, Little john, telluria.
Block mana generation
Proteus , Hel
Zocc , Merlin.
Hansel and Gretel does something similar but the hero hits itself and lost 50% of mana.
Def down / Elemental def down
Reduces the defense of the enemy. Can stack def down and elemental defense down for more damage
Frida, phanter, Grimm, Tiburtus, falcon, Jackal, almur
Reduces enemy attack.
Scarlet, Vela, Richard
Hope it helps you. Sorry if i miss something but is an extensive topic