Steer Clear deals 2 damage to target attacking or blocking creature. Steer Clear deals 4 damage to that creature instead if you controlled a Mount as you cast this spell.
Not legal in Alchemy, Premodern, Pre-EDH, Old School
Notes & Rules Information
If you controlled a Mount as you finished casting Steer Clear, it doesn’t matter whether you still control one as the spell resolves. Steer Clear will still deal 4 damage.