Defenders for MewTwo?
OK - MewTwo is getting to be more common.
So, you have to figure folks attacking gyms are now using Focus Blast MewTwos instead of Machamp to attack gyms a lot. It's now the best BlissLax counter.
I used to put in Espeons and Clefables as defenders to screw up Machamp.
What is the "hurt a mewtwo" defender to replace my Espeon? Obviously, psychic attacks aren't the best against MewTwo. Dark attackers are slammed by Focus Blast. Scizor maybe - at least it's fast enough to get off a charge move or two...
Well, we don't have much for the ghost side, and if we cut them out we only have Pinsir and Scizor... 2 defenders. We need 4 more so out of them if it's not a ghost/dark type, then best would be something resistant to fighting but that can use ghost/dark. Maybe Gardevoir, but its fast move being electric for some reason does not seem ideal.
I agree that Charged Beam is an odd choice, but at the very least it isn't resisted and generated high energy (15 energy per use!)
However, Confusion generates just as much with greater damage and STAB. It may be much slower, but that doesn't matter when defending.
I don't think any of these options are great. Pinsir and Scizor are still pretty frail - Pinsir will quickly die to Confusion as it doesn't resist it. More importantly, Pinsir's Bug Bite and Scizor's Fury Cutter/Bullet Punch are very high-speed, low damage Quick Moves, which, on gym defense, translates into mediocre damage and energy gain.
You really want slower moves for gym defense. This is why I think Gardevoir's such a great option. Snarl is the best Dark Quick Move for gym defense, opening up Houndoom and Absol for options, though I would argue their ability to counter Mewtwo would give them no room to counter anything else given their frailty.
Ghost and Dark types don't have a lot of the tools needed to deal with Mewtwo right now. The better option, in my opinion, is in low speed quick moves on strong generalists that won't die to one Focus Blast. This will exploit the weakness in that Focus Blast is a very poor Charged Move when used without STAB or SE, and Mewtwo doesn't have the bulk to survive long-period engagements.
Machamp is still the best BlissLax counter because it's faster than Mewtwo and has less awkward energy management.
But as for countering FB Mewtwo, Metagross and Gardevoir come to mind. Maxed FB Mewtwo takes 25s or longer to kill both of them even when they're only level 30. Steelix and Scizor are also decent but Scizor has the downside of absolutely melting against anything it doesn't resist, whereas Steelix is a pretty good defender. Finally, Umbreon also takes 20+s for Mewtwo to kill even taking SE from FB.
I'm looking into raising a Metagross. It threatens Fighting Types with bulk and Zen Headbutt, and it double resists Psychic among many other types. It is countered by Ghost and Dark sure, but Zen Headbutt and bulk should ward off Gengar, and Flash Cannon could be the answer to Tyranitar. It is clearly threatened by high-dps fire types and the now-relatively common Groudon, meaning that it would serve as more of a threat to high-level players that specialize than low level players that usually go in with their best generalist (low levels usually have widely accessible generalists, such as fire types [e.g. Arcanine, Flareon, Houndoom] and raid boss catches [Groudon]).
Gardevoir is definitely the best answer to Fighting types. Strong, STAB, effective Quick Move, double-resistance, and two great options for two-bar Charged Moves. Shadow Ball punishes Mewtwo/Alakazam, DG punishes fighting/dark/dragon types. Only problem is you can't have both of these Charged Move options at once.
Aggron and Tyranitar with Iron Tail are really not bad options for punishing a Mewtwo. If the attacker isn't ready to go with a Focus Blast, the relatively-glassy Mewtwo will have to take a long of punishmment before firing one off, and they absolutely will have to use a Charged Move to win. Moreover, both come equipped with early damage-window multi-bar moves, Heavy Slam and Crunch, one of which is effective against Mewtwo. However, Pokemon like this should never be in a gym without a strong Gardevoir or Dragonite.
Lastly, good Flying generalists will give Focus Blast Mewtwo a hard time. Focus Blast won't hurt too much and is neutrally not a good Charged Move, so the attacker will mostly be relying on Confusion and Psycho Cut. Given enough bulk, this leaves lots of opportunities to damage Mewtwo. This means bulky, strong Quick-Move-carrying options like Waterfall/Crunch Gyarados, or Dragon Tail/Dragon Claw/Outrage Dragonite.