Mega Blast (メガブラスト Megaburasuto) is an official term used to describe an kind of skill which requires this cost: [Soul Blast (8) & Counter Blast (5)].
Normally, Counter Blasting 5 damage means you can't use any other Counter Blast skills throughout the game. However, clans like Nova Grappler have access to effects that can flip damage back face-up for you to reuse. Additionally, other clans have more limited methods such as Bellicosity Dragon and Silence Joker. With some luck, a Heal trigger can help recover damage for you to use.
All units so far that have access to a Mega Blast follow a certain pattern. They are all Grade 3 Units with 10000 Base Power. They also all have a Vanguard-only skill which, at the start of your Main Phase, put one card from the top of your deck to your soul (Soul Charge) and activates an additional effect (commonly giving the activating unit +2000 Power for the rest of the turn) to help with the 8 soul requirement. Some of these units have additional skills (such as CEO Amaterasu). Most Mega Blast skills activates only on the Vanguard circle, although some can also be activated from the Rear-guard circle.
Originally Mega Blast skills were awkward and difficult to use, because very few cards had the ability to increase the soul, and most games were finished before one could reach 8 soul. Also, most decks were inefficient without heavy Counter Blast skills, and on top of that, staying at five damage until you could make one of your units hit made Mega blast units, especially [AUTO] ones, very inconvenient. However, with more support, more clans were capable of increasing the soul and unflipping or increasing damage, Mega Blasts have become easier to use.
Mega Blast units which can be used in the Rear-guard circle do not require a vanguard of the same clan. As such, it is possible to use units from another clan to help set up the Mega Blast, or to include them in decks based on a different clan. Be aware though that certain units, such as King of Demonic Seas, Basskirk, Unite Attacker and Top Idol, Pacifica work best in a pure clan deck.
If you're using a Mega Blast unit from a clan that doesn't have dedicated support for increasing the soul, you should use units that move themselves to the soul to help reach the required quota. Riding a second copy of the Mega Blast unit over the first can also increase the soul if the Mega blast unit is the vanguard. Similarly, if you're using a clan that doesn't have reliable unflipping skills, you should avoid using other Counter Blast units in your deck.
When choosing which units to include, pay special attention to their Soul Charge skill. Mr. Invincible and Kurama Lord allow you to unflip damage, letting you include some other Counter Blasts in your deck. CEO Amaterasu and Top Idol, Pacifica can control the cards that will be in your hand, giving you great flexibility, and they both have additional skills that give them higher power, so they can hit and use their Mega blast more easily. Dusk Illusionist, Robert has the same skill as Amaterasu, but lacks the extra power boost. All the other units have a flat +2000 Power increase for the turn, which is not quite so useful as many units now have higher base Power and the increase doesn't always amount to much.
List of Mega Blast cards
- Mobile Hospital, Feather Palace - [AUTO]
- Top Idol, Pacifica - [AUTO]
- Subterranean Beast, Magma Lord - [ACT]
- King of Demonic Seas, Basskirk - [ACT]
- Knight of Fury, Agravain - [ACT]
- Vortex Dragon - [ACT]
- Death Warden Ant Lion - [ACT]
- Stealth Fiend, Kurama Lord - [AUTO]
- Mr. Invincible - [AUTO]
- CEO Amaterasu - [AUTO]
- Demon Slaying Knight, Lohengrin - [AUTO]
- Knight of Purgatory, Skull Face - [AUTO]
- Unite Attacker - [AUTO]