Unblockable is a special ability in Magic the Gathering Tactics.
A figure with unblockable ignores enemy zones of control.
The unblockable ability allows for more movement, since a figure with it doesn't have to go around entire zones of control.
A figure with unblockable is still restricted by terrain.
Unblockable somewhat counteracts a flying enemies control of the board.
The threat of an unblockable figure is increased with movement. The more movement, the higher the threat. Spells and abilities that give more movement to a figure work well with unblockable creatures.
Unblockable works differently in the Magic card game than it does in Magic Tactics.
While the spirit of the ability is the same, the mechanics turn out very differently.
In the Magic card game, unblockable allows creatures to directly attack and damage the opponent (one of the ways to win).
In Magic Tactics, the unblockable ability allows slightly greater options for movement. This can lead to directly attacking the Plainswalker or creatures that are bothersome.
Since the mana cost is based on the Magic card game, unblockable is less powerful in the Magic Tactics game.