Tree form is a bad form that can be inflicted on the player by the polymorph other spell. Its most notable feature is that it entirely prevents the player from moving, but not from otherwise acting. Unlike most bad forms, it can be entered easily by quaffing a potion of lignification. While transformed into a tree, the player gains the following attributes:
- +50% HP
- +20+0.5×XL AC (+33 AC at level 27)
- 48% GDR
- +10 strength
- Unarmed Combat base damage is set to 12
- Bonus to to-hit
- Huge size (immunity to most types of constriction)
- Torment immunity
- The player's hunger is set to Satiated (gaining nutrition from the ground via their roots), and they don't hunger
- Cannot move, but can cast spells, use abilities, and attack
- EV is reduced to basically nil: (2 + size_modifier/2 + EV from Repulsion Field mutation, the same as when you are paralyzed)
- Cannot teleport without divine intervention (Lugonu's Bend Space ability works as normal)
- Cannot fly
- All equipment other than shields, weapons, helmets, and jewellery are melded.
Tree Form, while it provides several severe drawbacks (melding most equipment, inability to move or teleport, loss of EV), can be helpful in some situations. Players in Tree Form get a large boost to their physical durability, which may help them survive fights against strong monsters. Another notable effect of Tree Form is its complete resistance to all forms of negative energy, including torment; a battle with a powerful enemy that relies heavily on negative energy or torment can be greatly assisted by entering Tree Form. (Some good examples include ghosts of mature draconians, Menkaure, or shadow dragons).
Characters that have ranged attacks will likely have an easier time in Tree Form than melee brutes, simply because they will still be able to attack their opponents should they blink away. Also, characters that don't or can't use much equipment (Transmuters, trolls, felids) will be able to make better use of Tree Form than a character that relies on their artefact armour to round out their defenses.
Just keep in mind that being in Tree Form will not allow you to escape. Should the battle go south, your only option will be to wait until the transformation wears off and hope you can survive long enough to flee; a potion of cancellation can help shorten the duration of Tree Form in an emergency.
Prior to 0.15, players in Tree Form could not eat or drink.
Prior to 0.13, it could make you vulnerable to fire, and the AC bonus and the speed penalty didn't depend on XL.
Like most bad forms, this was added in 0.12