Thorn Bastion is a legendary major card out of the New mechanic pool. Bastion Field's ward reflects 25% of damage taken by everyone it covers; the ward is 80%.

You can take it once · it only turns up when your Special ability can actually use it · it can be offered for 0 of the 34 abilities.

Only one card can reshape that ability this way — this one, or Wide Bastion and Long Bastion. Take one and the rest are gone for the run.