The Succubus is essentially a glass cannon - she can deal high damage, but can fall quickly if left unprotected. Succubi should always be placed at the back under the protection of other units and Heroes so that she can deal as much damage as possible before falling in battle.
Succubi have the lowest attack, health and defense out of the three Heroes; however, they do possess the highest attack range of 7, which is on par with Iron Wheels. Succubi will benefit from a high-leveled weapon in conjunction with the most attack speed bonuses possible, so they can easily turn any unit they are focused on into shreds, including heavily equipped Behemoths and Berserkers.
They will also benefit from gems to help boost their offense. Succubi do not benefit much from defensive gems as with the melee heroes, so they are not needed. Health gems would be the only exception, but even then only for Adventure purposes because they use different forms compared to PvP battles.
The Succubi's unique medal is the Mist Medal, which helps the Succubi cast spells more frequently and dizzy her opponents. For each level added on the medal, she casts spells 3.0% faster and her attacks have an additional 1.0% chance of inflicting the Dizzy status on her opponents.
The Succubi's ability is Magic Flash, which randomly activates throughout battle. When this occurs, she has an increased chance to land critical hits for 4.0 seconds. The rate increases as the ability is leveled up, requiring spar and elements. This effect works in conjunction with force gems, who increase the damage dealt by these hits.
The Archangel set provides the Succubi with the Revenge ability, which summons a rain of fire that damages all enemy units on the field. Activating the set requires at least 3 parts from the set, with the best effect activating with all five pieces.
At level 45, the Succubus gets the Wee Devil as a pet when the Pet Shop is built. The Wee Devil provides a balanced set of effects compared to the Jungle Ape and Fire Cat, as both her offense and defense are increased as the pet levels up.
You can find an overview about all items here.