I'll add on Nidoking and Nidoqueen later
Viable Poison Types available in Kalos:
Roserade-Rather frail, but has good typing, movepool, and pretty good stats. It needs a Shiny stone to evolve into this forme, though, and takes friendship to get a Roselia from Budew.
Also, it learns all it's good moves in it's previous evolution, so be careful when deciding to evolve it.
Toxicroak--Note it's 4x weakness to psychic, and it's ability dry skin. It will take 1.25 from fire, and lose I eighth of it's health each turn in sun, but that shouldn't be much of a problem ingame ... Unless it has the ability Anticipation...
HMs: Cut, Strength
Crobat-evolves through happiness, and so takes a long time, but is probably worth it. It has good speed, and decent Atk.
*Tentacruel*--Rather frail in physical defense, but fast, and has decent SpA and good SpD
HMs: Cut, Surf, Waterfall, Dive
Drapion---Can take a few hits, and can dish it back out very hard, especially with it's ability Sniper, which x4s every critical hit, plus it's High Crit. ration moves. It's other ability, Battle armour, which prevents critical hits from being used against it, is also useful.
Gengar--high speed and SpA, and has a Mega Evolution, but you need to trade to fully evolve it.
Also, It do not evolve Gastly into Haunter before it learns Shadow Ball
You should also replace boldore, with Aegislash, if you're worried about the fairy gym, since you need a steel type,and Gigalith requires a trade, and is kind of weak. Sigilyph is also iffy.
Go here for Aegislash movesets. Be aware, however, that some of them are intended for competitive, not ingame.
Aegislash is a very versatile, and powerful Pokemon, however, because of it's ability Stance Change, it's once impregnable defenses are now lowered to 50 when you attack, shifting the 100 stat points onto the offenses. You have to wait for the battle to end, or use King's Shield to switch back, but overall, it's pros outweigh the cons.