I'm gonna leave some info here despite me not playing Bass anymore. Two years of knowledge should be enough for forming a meta game and I was fortunate to play two very good Christie players in UK and I also spent time in the lab testing buttons against each other.
vs
4-6
Generally, this is what I consider to be the Gief-dictator/Hugo-Chun/Potemkin-Zato1 of this game except the rather one-dimentional approach a Bass player needs to have in regards to this MU.
Most often used Bass tools will be p+k, pk (a whole lot), 6p, 6k (for beating crush attempts and priority mostly) 2p, 1p (mostly for advantage, resets and mixup) and true mids with tracking like 66p and 214p. The decent tool he has for mid range is 66p+k which should be used only sparingly and as a whiff punisher since it can be easily crushed or SSed. Similar case for 33p as a whiff punisher except that it's also used to beat crush attempts as a true mid or situations like 3p+k transitions.
For Christie on the other hand, it's pretty much the case of pretty much having the liberty to use anything from pp string mashing to mid string 2/8p+k transitions until you're punished, to baiting a range of things at mid range with 214p to just crushing pretty much most of his pokes with 3p or 33p. 6pp at midrange is also a given with 9p for tracking and kp to beat slower crush attempts. As a mid weight she also benefits from opportunities to get out of pressure easily from his blender or his 6h+p mixups.
The guessing is mostly in the Bass player's court as even after a throw punish, he's guessing and opting for a different set of tools as the regular pokes like 6p, 3p, 3k, which are pretty much the pokes with good priority can be easily crushed and SSed. At +10, it's still normal to treat the situation as neutral and more often go for a hail Mary than sticking to the normal meta game. This is one of those things that he doesn't have to deal with in MUs like the Sarah MU once he has the ball in his court, since she doesn't have those get out of jail free cards.
For Christie players, having MU knowledge means that even at major frame disadvantage (if it's not throw punishable that is), they have a chance to avoid most mid attempts. Though if they're really looking for high damage, they have to look more for counter hit launchers and building up thresholds. Throw punishing holds, even psychologically may not convince a Bass player to stop attempting to hold you however, as Bass players are aware that Christie has the weakest throws outside of her wall throws and most are willing to take the damage. His holds have good damage and a well timed mid P hold is a good momentum shifter and his mid K holds are also no joke, so it's usually well worth the risk.
An effective tactic which Christie players opt for are long string delays and SS transitions. The first one is pretty effective as it can throw people off often, but the latter can be risky against a player who knows the MU and can react and punish for good damage with 6p.
One other thing that shuts down 2/8 p+k transitions is his PK which kills SSs very well and gives him a free launcher. The string transitions are also decent but very limited, which always leads to Bass players having to improvise with limited tools.
In terms of range game, Christie can stick to close range while Bass has to go back and forth between close and mid range to not get overwhelmed. His game mostly about forcing a mistake from an opponent or picking up on something and punishing that.
Generally, this MU isn't that bad, but at times it becomes tedious with Bass players need a good knowledge of what they're going against beforehand, which turns into an academic study. My advice to any Bass player is to put in lab time if they actually care and ask other Bass players for help, because this one of the more time consuming MUs in this game, an most Bass players play the character differently. Christie players on the other hand don't really need that much to get started as Bass' tools are limited. Be random.
Bass players, be very very patient and develop your reaction times.