for those of you who don't know, the "healthy boost" is a battle sprite that comes with the seraphynx. (I don't know if the drakon or maskiwraith has it too) and it gives you extra health. the only problem with it is that the effect only takes place after you go to another floor. and the only place you can change battle sprite perks are at the beginning of the floor, so if you choose "healthy boost", you have to go through a whole floor before the effect takes place, and you are pretty much stuck without a perk for that floor. idk if this was intended or not, but I think this should be changed so the effect applies immidiatly.
http://forums.spiralknights.com/en/node/85442
It's also an exploit.
It's a battle sprite PERK, not a battle sprite that comes with the Seraphynx. That'd be way too OP. Imagine a sprite for YOUR sprite...
But anyway, all sprites get it, and it eventually gets better over time as you level up (with luck).