Anyone who has played Gold,Silver,Crystal and tried to catch the roamer legendarys knows how much of a pain in the a$$ that was but for some reason it took forever to catch Entei when I played them. Roamers in general were a b!#%& to catch but in X Y it was so annoying to find the LB 10 times b4 being able to catch it. Still not as bad as my Entei experience though.
I spent forever in the Safari Zone in RBY trying to catch Tauros. It was my 151st Pokemon to complete my Pokedex. It literally took me a week or two worth of recess to catch that thing.
I remember trying forever to catch Mewtwo. Eventually froze him using Arcticuno. I had him down to a sliver of health, but still no luck. Out of frustration I had Hitmonchan use strength. It must have done 1 or 2 HP of damage and I caught it within a couple more tries. All in all, I didn't spend that much time on him.
Moltres was the last non-safari zone catch for me, so I used my master ball on it.
My game battery died a few days later, so I only got to bask in the glory of catching them all for a few days.
I have to agree with the topic creator here--The Regis (particularly Regice) in R/S/E kicked my butt! I cannot count the number of times I threw my GBA down in disgust. To this day the Regis give me a bad taste in my mouth, lol.