Unlike most other Supremes, Leaders will be the focal point of building your Team - if you choose a Leader, then it is likely you will be choosing a particular Faction or Alignment of models to select around them.
A Leader typically has HP equivalent to Level 2 Tanks, give or take. However, they usually have a better set of defensive Traits. So what you have is a slightly more durable model than most combat-focused Level 2's, yet at a higher cost (Level 3 for the most part; ARC's Primates of Power are something quite different).
Because Leaders offer a mix of Team boosts, their array of Attacks is usually more limited than the combat oriented roles such as Blasters and Brawlers, but most Leaders can pack a hefty punch one way or another.
Where things get very interesting is through Leader Cards, which is why these Supremes have the cost that they do. These cards offers bonuses and extra resources such as AP or Power Up dice; they allow you to customise how your Leader will shape your Team.
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If the Leader meets the requirements they may also take a Faction card which usually provides a pivotal boost to the Team; but timing is everything as these are often one-Round deals.
Leaders pack in a lot of utility for a Team. They may not be the hardest hitting models, but they can unlock massive potential for their Teams, and now with Pulp City SE they are a lot easier to bring to the table than before.