Just spam b for this while walking around or use this method below and work on multiple cheevos at a time.
Here is a full guide on how to get the ultimate, evade, block and parry achievements quickly! A visual guide and explanation is below if you like written more. If this does help I implore you to checkout my other videos for this game. I recommend using the Drizzt character which can be chosen in camp by clicking pause. From the camp map select Trials of Tempus(Tutorial). Once loaded do all objectives listed until you reach the objective about locking onto targets. Don't do that objective rather you should notice if you spam RB you can get your ultimate in like 5 seconds. Once obtained use your ultimate and while it is active just evade for that achievement. Once its over spam RB on Goblins till gotten again. Now repeat this cycle until all 100 have been done. It will likely take around 20-30 mins. Once done or before this you can get your blocks in and can get your parries in if intrested although you must do 500 parries which will take awhile and is probaly better to do mid game and finish your last ones there.