Lone Druid

Spirit Bear
Spells last as long on Spirit Bear as they do on heroes.

Various mechanics
Mana
 * Unlike Animal Courier and Flying Courier, Spirit Bear can obtain mana from items directly increasing mana pool.
 * Natively Spirit Bear seems to have a bit less than 0.1 mana regeneration, modifiable by % mana regeneration items and direct mana boosts.

Items cooldowns
 * Sylla and Spirit Bear operate on 2 completely separate sets of cooldowns.
 * Once item is activated, cooldown does not change upon moving to other inventory (hero has cooldown on item and simultaneously instance of item has cooldown of it's own), example:
 * Lets say you have 2x Dagon,
 * Use 1st on Sylla and 2nd on Spirit Bear,
 * When you move both to Sylla's inventory, cooldowns are still displayed separately,
 * Let's say you put 3rd Dagon into Sylla's inventory,
 * You see two Dagon displaying same cooldown (1st uses both hero's and item's cooldown while 3rd displays only hero's cooldown), while 2nd is displays it's own cooldown,
 * When you move 3rd Dagon into Spirit Bear's inventory you will see it displaying same cooldown as 2nd instead of 1st.

Hand of Midas
 * Double Hand of Midas is a bug (should be courier version) and will be fixed shortly.

Gem of True Sight
 * Gem of True Sight does not reveal invisible units when held by Spirit Bear.
 * Spirit Bear still drops it on death.

Aegis of the Immortal
 * Spirit Bear cannot pick up Aegis of the Immortal, but can attack (destroy) it.

Runes
 * Spirit Bear can destroy runes, as can any other unit. However, Spirit Bear can also use runes, which is a glitch.