250.
Use your Skills until you're out of SP. This one can use its own skill twice to restore 75 HP once it gets below 50%.
You should also grind in the room before that, or even earlier, because they're both still at level 2! This game is much easier if you aren't avoiding battles ALL the time, because this is only the 2nd of over 10 required, and several optional bosses.
I strongly suggest running away from the single Bug enemies on the very first map when Ben is solo, but then pushing through The Bridge and outside the Cavern to get inside the Cavern to the waterfall room. Then grind up to level 4 or 5 while near the healing save statue.
Run back to the house to rest if necessary before you get Sunny. Also have to go home to learn the girls' PowerSkills from the plants you get in Sunflowers Meadow before taking on the boss battle there.
