Magmar is imo, a shaky check to Jynx. A weakness to Stealth Rock and other form of entry hazard with no recovery aside of Wish(from teamates), its low physical defense even after an Eviolite boost, and being easily 2HKO by Psychic from Jynx on the switch with some entry hazard up (which is easy to do in a tier where Rapid Spinners are bad (except Wartortle, but its mostly used on stall team and has to play mindgames with foresight to get a spin off)) or some prior damage, which isn't hard to do.
Ofcourse, Magmar will win against Jynx if it safely switch on it with full health, but it can't stop Jynx from switching out, unlike Skuntank (Pursuit/SuckerPunch mind games), Liepard (Pursuit/U-turn), and other Pursuit users. Finally, while Vital Spirit is cool to avoid Lovely Kiss and such for a Jynx's check, the same can be said by using Lum Berry or Sleep Talk on some of your Pokemon if you are scared to make one of them useless by letting them fall asleep.
Ofcourse, Magmar will win against Jynx if it safely switch on it with full health, but it can't stop Jynx from switching out, unlike Skuntank (Pursuit/SuckerPunch mind games), Liepard (Pursuit/U-turn), and other Pursuit users. Finally, while Vital Spirit is cool to avoid Lovely Kiss and such for a Jynx's check, the same can be said by using Lum Berry or Sleep Talk on some of your Pokemon if you are scared to make one of them useless by letting them fall asleep.