Thunder Strike

Instant

Target creature gets +2/+0 and gains first strike until end of turn. (It deals combat damage before creatures without first strike.)

2010-08-15:
Thunder Strike can target any creature, even one that already has first strike or double strike. (If it affects such a creature, it will, in effect, just give it +2/+0.)
2010-08-15:
If a creature doesn’t have first strike, granting it first strike after combat damage has been dealt in the first-strike combat damage step won’t prevent it from dealing combat damage. It will still assign and deal its combat damage in the second combat damage step.