Explosive Blast is an Mastery Wizard skill unlocked at Level 19, blasting a small area for high damage.
This skill works differently than almost all other Wizard abilities. It's a Nova-type attack that radiates out from the Wizard, and it's triggered like a time bomb, with a delay between the trigger and the detonation. A Wizard will need to learn to use it strategically, by lighting the fuse and then moving into close proximity for the explosion.
Of course it's dangerous to be close to monsters, which makes this something of a specialty ability -- great fun for some players, but ignored and dreaded by most.
Explosive Blast in action.
The Wizard conjures volatile gasses into the physical realm, which ignite with oxygen and create a powerful blast in a very limited space.
Refer to the Explosive Blast rune effects article for thorough descriptions of all five rune effects in this skill, including screenshots, videos, strategy tips, and other related information.
<skill class="Wizard">Explosive Blast</skill>
<skill class="Wizard" rune="Unleashed">Explosive Blast</skill>
<skill class="Wizard" rune="Flash">Explosive Blast</skill>
<skill class="Wizard" rune="Short Fuse">Explosive Blast</skill>
<skill class="Wizard" rune="Obliterate">Explosive Blast</skill>
<skill class="Wizard" rune="Chain Reaction">Explosive Blast</skill>
This skill is basically a short-range nova centered around the Wizard, on a short time delay. Since the Wizard can move after activating it, she can select it, run into the midst of a pack of monsters, then laugh when they go boom. The spell's delay (about 1.5 seconds) makes it unsuitable for emergency use, and its short range makes it difficult to use without getting pounded on.
The following Wizard passives provide a benefit to Explosive Blast, runed or not:
<skill class="Wizard">Glass Cannon</skill>
<skill class="Wizard">Critical Mass</skill>
<skill class="Wizard">Arcane Dynamo</skill>
Explosive Blast was first seen at BlizzCon 2009 in the gameplay demo, where it was on the Conjuring Skill Tree at Tier III. Originally, the Wizard targeted a specific location, and after a short delay, the blast went off.
By BlizzCon 2010, the mechanics had changed; the blast was focused on the Wizard. It was also moved to Tier 2 after skill trees were removed. It was one of the Wizard's starting skills in the gameplay demo, and Flux found it entertaining:
It’s basically a short-range nova, on a time delay. You click it, and after 1.5 seconds (at level one) it blew up, dealing fairly substantial physical damage. The time delay made it unsuitable for emergency situations, but if you got used to the timing it was fun to click midway through a battle, knowing it would blast a moment later and finish off the enemy.
Skill tiers were removed for the July 2011 Press Event, allowing skills to unlock steadily from levels 1 to 30. Consequently, all skill levels were adjusted and Explosive Blast became a level 14 skill.
The Diablo III Beta started in September 2011, and while it ran, all of the skills continued to undergo extensive iteration. Skill changes varied from changing the levels the skills are unlocked, to changes in resource cost, damage, and even function. A few skills were removed altogether, and a few new ones were added. Also, the entire skill system received an overhaul with the Beta Patch 13 update in February 2012, with physical runes replaced by rune effects that automatically unlock at various levels for the different skills.
Explosive Blast was moved to level 15 during the beta. With the Patch 13 changes, it was classified as a Mastery skill and bumped to level 19. For March's Beta Patch 14, the damage done by this skill and its rune effects was reduced quite a bit.
See the Wizard skill archive for more details on previous versions of Explosive Blast and other Wizard skills.
Explosive Blast can be seen in action on video here:
You can find pictures in the Diablo III screenshot and picture gallery: