I just have reacted about Cannon ability because there are in fact a lot of other abilities as bad as it. For example, when you use Autorun to do something else at the same time ALL Solar Blast abilities are completely useless (+X% Shine cristals drop rate, +X Sun Nodes, +X% to Solar Blast). On maps without any Pest Nest several other abilities are completely useless (-50% Damage, Change them in Recovery Node when you walk on them); the same when there are not any Recovery Node (x2 or x3 Recovery)....

So, just to say there are a lot of other abilities who are more or less often useless. Cannon ability is bad, sure, but IMO it's certainly not the worst, by far (and Gardenia is a real beauty but that's not the question). Anyway I don't take the point of view of a veteran player with a full Set of 5*/6* maxed (20+ Knights), because in that case you can consider almost all abilities become useless anyway.

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Oh, and yes, the Cannon ability works with Fireworks as well, and is given to all your Squads.

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In fact Cannon ability seems even better than expected, or there is a tiny bug. I have one team with Gardenia (the only one I have with this Ability) and a Helper without this Ability, and when I farm the Reissue #8 mission 8 all the Teams trigger 2 shots (as expected) but my Team with Gardenia triggers 3 shots!