Shadow Scizor

Shadow Scizor is a solid pick for both Bug and Steel Type damage, though its comparative performance is definitely better with the former due to the competition in the Steel meta. Not a top performer, but also not the worst investment if you're desperate for a Bug and/or Steel Type attacker, with its dual-typing giving it additional utility.

Best PvE Offensive Moveset

• Fury Cutter and X-Scissor offer the highest DPS when facing Psychic, Dark, and Grass-types
• Bullet Punch and Iron Head are the preferred set for dealing with Rock, Ice, and Fairy-types
• Night Slash is underwhelming; a three charge move with a longer cooldown and does not benefit from STAB, only offering additional Ghost coverage

Best PvE Defensive Moveset

• Bullet Punch is on par with Fury Cutter, both having similar coverage or lack thereof.
• X-Scissor is clearly superior to Night Slash; both are three charge moves with similar DPS, but the latter's cooldown is significantly longer, making it easier to take advantage of dodge windows.
• Iron Head is often better than Night Slash, offering higher DPS at a shorter cooldown despite being a two-bar charge move, although the latter offers wider type coverage.

Bullet Punch tends to be preferred over Fury Cutter for its higher damage output, as Scizor's Charged Attacks aren't particularly impressive to be worth the increased energy gain. They're also mostly cheap enough anyways. 

Night Slash is Scizor's cheapest option and provides coverage against Steel-type Pokemon. X-Scissor is a wonderful STAB move, though Bug is often questionable offensively. Trailblaze smacks Water-type Pokemon and provides an Attack boost. Iron Head is often redundant with Bullet Punch's damage output.