This version of Chesnaught is a 180HP Grass Type Pokemon. While it is usually a Stage 2 Pokemon, because it is an EX, Chesnaught EX is a Basic Pokemon. It’s weak to Fire, like most Grass-type Pokemon are, and has a very hefty retreat cost of 4.
It takes a bit for Chesnaught EX to get going, as his first attack Pin Missile requires 3 energy to attack. Fortunately, it only requires one Grass energy, so Double Colorless Energy may be used. When you use Pin Missile, you flip 4 coins, and the attack does 40 damage for each heads. It’s an okay attack with a wide variance. Still, potentially dealing 80, 120 or even 160 damage is very powerful for only three Energy.
Its second attack, Wild Tackle, costs two Grass energy and two colorless energy. It deals 120 damage, but it does 20 damage to itself in the process. Overall, it’s not a bad Pokemon, especially for one that’s readily available in a promotional tin. It's fairly playable, especially with how much HP this guy has. You can even play him on your very first turn. He’s certainly not one of the more powerful EX cards out there, but he’s a fairly decent tank.
Picture courtesy of the Bulbapedia from Bulbagarden.