Hey, all. I've been wanting to contribute to these for a while, and I co-main ZSS and Fox, so I figured now would be the best time to make my appearance.
![Zero Suit Zamus :4zss: :4zss:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
vs.
![Fox :4fox: :4fox:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
Most of this will be speculative and based on my experience with both characters, since there aren't many Foxes in my area or on Anther's Ladder or For Glory, and I usually choose to do ZSS dittoes when I encounter one of those. However, there are some points that need to be made.
Point 1: ZSS is a very fast faller that is also light, making it hard for Fox to combo with U-tilts or Double-Jab. U-tilts can work to combo into themselves, but only at low-mid %s like 30-40%
Point 2: All of ZSS's aerials outspace all of Fox's. B-air, F-air, U-air all outrange Fox's horizontal aerial approaches. Fox's best bet when approaching horizontally is to hope to trade with a F-air and catch them out of hitstun if you can. Otherwise, Fox's U-air is his most useful aerial as ZSS' only downwards aerial hitbox is D-air, which can be baited out and punished. This, however, should only work a few times, as ZSS can just as easily Flip Jump away or U-tilt after D-airing (this surprisingly does work because of D-air's admittedly stupid lack of landing lag and U-tilt's fast startup and intangibility). Fox's strength in this MU is catching ZSS' landings. Flip Jump can be punished after a certain point when the Kick becomes impossible or if Fox can read the Kick. ZSS will usually try to cover her landings with N-Air or B-air. Fox can SH FF over these and punish with N-Air or D-Air, but he MUST be wary of ZSS' U-tilt's fast startup and intangibility.
Point 3: ZSS' recovery has many facets to it: Flip Jump, Tether Grab, S-Special (A 2nd tether grab), high jump height, Boost Kick, and Flip Jump wall jumps among them, whereas Fox has only Fox Illusion, Fire Fox, and his jump. While ZSS's thether grab and Flip can be punished hard (FF F-air on either, U-air or B-air for Flip Jump), it makes for a 50/50 read, and even then the ZSS can simply use Boost Kick, which is harder to punish (Fox must use B-air to do so). ZSS can more easily punish Fox's recovery, using B-air, F-air, or N-air to catch either option on reaction. (This is speculation, but ZSS could potentially use Plasma Whip to do a semi-spike on Fox Illusion or Fire Fox, it'd need testing.)
Point 4: ZSS has very dangerous OOS options in U-tilt and Boost Kick to respond to Fox's Dash Attack, misspaced N-Air, or landing D-Air should the Fox attempt a kill setup on shield. I'd recommend Foxes try their best to perfectly space N-Air or B-air on shield, or simply back off and shoot lasers from outside of Flip Jump Kick range. In addition, Fox loses combos out of his grabs at around 70%, and has to rely on catching landings or gimps. This removes one very important shield-countering option.
Point 5: Fox has good OOS options as well, in U-tilt, Jab, jumping N-air, and jumping D-Air, but all of these require ZSS to misspace her on-shield options in B-Air, N-Air, or F-tilt. (Any use of ZSS' Flip Jump or Flip Jump Kick on shield should be a punish for Fox with an aerial or caught landing.) In addition, ZSS's Z-Air is the epitome of safe-on-shield, but if the ZSS gets too trigger-happy with it, Fox can use his speed and shorter-than-average frame to run under the tip, the damage-dealing portion, and punish with whatever he sees fit. (I'd recommend Dash Attack or Dash Grab at low %s for combos, U-Smash at mid-high %s.)
Point 6: ZSS' D-throw>Uair is an easy stock off of Fox at %s above 110% and below 140%, otherwise it either may not kill or may be escaped. Fox's answer to this is to read when the ZSS will fish for a grab and punish HARD. ZSS' grab frame data is her WORST flaw. I'd heard somewhere that a whiffed ZSS grab lasts about as long as Ganon's U-tilt. Short-hop to avoid the grab and charge up whatever smash attack or set-up whatever combo you want. In speculation, times to look for this grab should be 0-40% (getting grabbed at the later end of this range can mean U-Air>U-Air>Boost Kick and a stock) and 100-140%.
Point 7: All of ZSS' Special moves are near useless against a smart Fox. Paralyzer shot can be reflected at point-blank range for an easy punish, but any further than point-blank means the ZSS can just as easily avoid the reflected shot and punish you simultaneously with a Flip Jump Kick. (In speculation, I recommend jumping over the Paralyzer Shot or backing off and shooting lasers from outside of Flip Jump Kick range instead.) As far as I know, every ZSS will try to Flip Jump Kick a predicted Reflector at least once on every player or character that has one. Fox can read this and punish accordingly. Plasma Whip is a very niche move and can also be punished hard. Flip Jump and Flip Jump Kick are very often telegraphed and are not safe on shield. To my knowledge, just using Reflector will stop the Flip Jump, but not the Kick. If Fox can properly space his on-shield options and/or cross up ZSS in her shield, Boost Kick should not be a problem.
TL;DR: ZSS wins whenever she has control because her aerials outspace Fox's and Fox is much easier to toy with off-stage. ZSS has a slight advantage in the neutral because of her safe on-shield options and dangerous grab, but that grab is just as dangerous for her as it is to you (because of its lag). Fox, however, wins greatly as long as he keeps the pressure on. ZSS has few safe, and no unpredictable, landing options and absolutely dispises having the disadvantage while she is in the air. Fox, on the other hand, loves keeping his opponents in the air. IMO this is a very momentum-based matchup, but ZSS has more tools to keep momentum. Solid
60:40, maybe
55:45 ZSS' favor.
Please let me know your thoughts on my write-up, as this is the first major one I've ever done. Also, I'd love anybody to point out flaws in my argument, as I am far from well-versed in this MU.