The Super-Block Meter is a gameplay mechanic of Plants vs. Zombies Heroes. At every attack, the Super-Block Meter charges, and when fully charged the attack is blocked and the player receives one random superpower from his/her hero's superpower kit. The superpower can be used immediately for free, or turned into a 1 or 1 (depending on the side) card to be used at a later turn.
After every hit, there is an equal chance of charging one, two or three bars of the block meter. The meter can only block three times before being destroyed, and the only way to attack the heroes without raising the meter is via the Bullseye ability.
Even though it is based on odds, it is possible to turn the Super-Block Meter in your favor. If the adversary is full of low attack troops, like the Imp or Peashooter, it is actually best to let them attack you, making the meter fill at the lowest amount of health possible, due to the high utility of superpowers and to stop the opposing hero from replacing those weak troops with stronger ones. Also if there is one very powerful troop and the meter is almost full, let it attack so you can survive another turn, which may be the key to victory.
Insta-Blocks are the most deadly outcome if your opponent is lucky enough to get it. This can easily result in your early defeat if you are unlucky. Because this is a luck-based occurrence, there is not much the player can do to get back when this happens, unless the opponent is unlucky and blocks a weak attack and gets a bad superpower card.
The best ways to counter this mechanic is with the Bullseye ability, which is available on both sides, although on the plant side this is not very useful as the plants with this ability have very low strength points. If you see this ability, don't let the troop attack the hero, as there is no positive outcomes out of it. Another counter is the Shieldcrusher Viking, as its attack depletes the whole meter. As it is a legendary card, the odds of encountering it on multiplayer are very low, but some single player missions may have it, so if it appears when playing as plants, destroy it as quickly as possible.
—Devin Low, Creative Director and Lead Designer, Plants vs. Zombies Heroes
Insta-Block (called Mega Block prior to version 1.4.14) was a mechanic that existed in older versions of Plants vs. Zombies Heroes. In those versions, the player had a 5% chance of receiving an Insta-Block whenever struck by a non-Bullseye attack, which would fill the block meter immediately regardless of current charge. It was removed on update 1.6.27, as PopCap decided that the mechanic introduced an unnecessary layer of luck to the game and created too many unfair situations.
- When a hero has at least 10 cards, he/she cannot block damage even if the meter is full. This is because a hero cannot gain any cards if he/she is holding 10 or more cards (except cards from Bounce effect) and Super-Block gives the hero a superpower trick card.