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Wall of thorns
druid attack 5

A thicket of briars confounds and traps your enemies.

area wall 8 within 10

Effect: The user conjures a wall until the end of his or her next turn. The wall can be up to 4 squares high and must be on a solid surface.

The wall provides cover. Each wall square also blocks line of sight except for creatures adjacent to that square.

When a creature starts its turn within a wall square or enters a wall square, it takes 1d10 + the user's Wisdom modifier damage, and ongoing 5 damage (save ends). A creature can take this damage only once per turn. It costs 3 extra squares of movement to enter a wall square.

Sustain minor: The wall persists.

Wall of thorns is a 5th-level druid daily attack power. It creates a wall that impedes line of sight and movement. Creatures that start a turn within the wall or move into the wall take damage and also take ongoing damage. The wall's conjurer can sustain it with a minor action.[PH2:88]

The December 2011 update limited the damage dealt by persistent effects created by a number of powers, including wall of thorns, to once per creature per turn. This change was made to prevent characters from using forced movement in and out of an effect's area to deal large amounts of damage.[U :12/2011]