The Treble Boost was first introduced in Megaman & Bass and later made its re-appearance in Megaman 10. Of course, it was toned down signifigantly from Bass’ appearances as a boss in MM7 and MM8, the latter of which was fueled by the Evil Energy. This ability allows Bass’ robo-hound Treble to fuse with his master, allowing free-flight as well as a spread shot (as well as turning a nice shade of purple!). The spread shots do double the damage Bass’ shots normally do (equal to Mega Man’s), and give you some extra coverage. You can even hit a single enemy with all 3 shots, although this certainly requires a bit more precision, as you may just end up flying into the very thing you were trying to avoid. This also essentially functions as a combination of Rush Jet and Rush Coil for Bass, although the Treble Boost drains energy faster than either.
In Megaman & Bass, this upgrade had its uses, although it generally wasn’t necessary unless you were trying to save time or grab a few otherwise unreachable CDs. It became a lot more practical in MM10, despite the game already feeling easy with Bass’ standard mobility. There were a few situations where you could use this to navigate certain segments of the game with much less difficulty (see: Commando Man), and it was there in situations as a replacement for Rush/Proto Coil. It also had a rather useful property; if the Treble Boost ran out of energy, your buster used the exact same mechanics as Mega Man’s! This means that it was just as strong as his blue counterpart’s and could also be fired by moving. Combined with the dash mechanic, it almost feels as if you’re playing as X!
Overall, the Treble Boost was a pretty decent upgrade, but I personally don’t find it as fun to use as the variations Megaman has had (i.e. Rush Power). The time limit certainly counts towards this, and if it weren’t for the CDs and the use of Megaman’s buster in MM10, I’d really have no motivation to use it other than when I just feel lazy. 6/10.