The "big '19'" explanation – episode 6 – Scizor (part 1) – Typing
Everyone knows Scizor has a great type combo: Bug/Steel.
However, Steel helps Scizor the most. Scizor's most resists come from Steel.
Bug is still great, which helps some Steel's weaknesses.
The only type that counters Scizor is Fire, and it does DOUBLE super effective damage to Scizor. That is certainly an extremely big pain, which prevents it from being a good gym defender.
Everyone wants a moveset of the same type because:
Bug's advantage: Grass/Psychic/Dark
Steels' advantage: Ice/Rock/Fairy
None of them are the same, however there are exceptions like Jynx, which receives single super effective from both of Bug and Steel.
Dark Pulse is not good, Bug (notably X-scissor) covers most things and gains STAB advantages.
Part 2 will come tomorrow!
Answers
I am not sure if understood correctly, so i want to point out this aspect:
Bug- and Steel-Attacks are (single) super effective againts tyrannitar. But this does not make a bug-steel moveset double effective, it is just single super effective with both moves, quick and charged.
Fighting type is double super effective against tyranitar.
