Apart from a few pixels on it's overworld sprite, BIG STRONG TREE looks identical to every other tree in VAST FOREST. It can be identified as an enemy due to briefly turning transparent when the party flees from a battle.
A gentle breeze blows across the leaves.
BIG STRONG TREE will always do nothing as it has no programmed attacks other than remaining stationary. This makes it one of the enemies that doesn't use any of their skills but DO NOTHING.
The tree deals no attack damage but its defense is practically infinite, and it is unable to feel EMOTIONS. Damaging it almost always requires critical hits or attacks which ignore defense. Certain attacks and items will deal damage to the tree:
JACKS purchased for 25 clams (40 JACKS required to kill the tree, 1000 clams), which deal small damage. BIG RUBBER BANDS or normal RUBBER BANDS deal more damage than JACKS, and can be bought slightly later than JACKS can.
OMORI's skill STAB, which ignores defense when he is SAD. For the most effect, use items or skills to make him MISERABLE.
AUBREY's skill POWER HIT, which ignores and reduces defense. For the most effect, use items or skills to make her ENRAGED.
KEL's skill RUN N' GUN, which can deal huge damage if KEL's SPEED is high enough. For the most effect, make him ECSTATIC, use COFFEE on him, and give him a SPEED-increasing charm/weapon such as the CHICKEN BALL.
KEL's skill RALLY, which can fill up the party's ENERGY without needing to be hit. Once ENERGY reaches 10, OMORI can RELEASE ENERGY to deal damage.
Party members can be equipped with LUCK-increasing charms to raise the chance of critical hits. HERO and KEL's JUICE-restoring skills are also useful in case any party members run out.
The Big Strong Tree's location (Notice the few additional pixels on its sprite compared to the other trees).
Big Strong Tree's overworld sprite.
Once it is defeated, the BIG STRONG TREE will disappear and not respawn.
BIG STRONG TREE is one of the few enemies that cannot physically harm the party, as it has no skills that involve attacking them. The other enemies that share this trait are the GHOST BUNNIES and MARI.
The BIG STRONG TREE has an ATTACK of 999. This is shared with MR. JAWSUM, who also doesn't do anything in-battle other than turn his GATOR GUYS angry or summon more to assist him.
The upward-facing angle this tree is seen from is similar to SUNNY's view of the tree from which MARI was hung. The flavor text in the battle also alludes to this scene, specifically, SUNNY distracting himself by looking up at the leaves.