Unhasty

From the Comprehensive Rules 4.0:
The Free Peoples player cannot assign a character with this keyword to a skirmish unless it is at its home site (see ally) or when a Gandalf-Culture card allows it do so.
Shadow players may assign any leftover unassigned minions to unhasty companions.
See also Assignment phase.

One of the Gandalf cards to let your Ent Ally skirmish is Stump and Bramble.

List of all Characters with the Unhasty Keyword

Loaded Keywords
Numeric Damage + X Defender + X Ambush X Hunter X Toil X
Non-numeric Aid Archer Enduring Fierce Lurker Muster Sanctuary Ring-bearer Unhasty
Item Class [Classless] Support Area Armor Brooch Box Bracers Cloak Gauntlets Hand Weapon
Helm Mount Palantír Phial Pipe Ranged Weapon Ring Shield Staff