Terrakion is an example of how faithfulness to the video games can backfire.
The good news is we have a Basic Pokémon with maximum HP and a solid-Type (Fighting). The Weakness is manageable (as far as I know, we still lack a good, Grass-Type attacker). The lack of Resistance is disappointing but also expected (so few Pokémon receive it), so no real harm there. The massive four Energy required to Retreat will be a pain, but at least it makes Terrakion a legal target for Heavy Ball.
The Ability would be better if the format wasn't so... homogenous. Yes, Darkrai EX is a fairly heavily played, as is Sableye... but that is two Darkness-Type Pokémon out of how many that have been printed? That extra 50 points of damage to them is still fairly nice. Where the card really fails is forgetting how to calibrate an attack. Perhaps they thought the rest of the card was too good?
To be clear, the attack has a lot of problems. Even though I can remember when 80 would be a good return four Energy, it now is at least 20 short and even that is the bare minimum (pretty unlikely to work since this card lacks built in Energy acceleration). When you are in a format of OHKOs and 2HKOs... you should only discard Energy when you can discard a lot of it or with a low Energy attack.
If the damage output was high enough, it would just be an occasional bonus and often wasted effect. Here it just reminds you that you aren't hitting hard enough except to OHKO Darkness-Type Pokémon that are Fighting-Weak (which you actually overkill by quite a bit; also wasteful). Pretty clear to most that this card needed a lean, mean, inexpensive attack; preferably mostly or all Colorless in requirements. That would turn this into a Darkrai EX slaughtering machine. It wouldn't be as good against most other Fighting Weak Pokémon as say the preferred Terrakion (NVI), but it would be something.
what else could you ask for?
