Yeah, I usually just edge guard Samus to death. Needles kill her bomb stalling game and her up-b is very linear. When she's getting close just go in for the edgehog. Drop off and Bair her if she tries to drop into Up-b range, and do the same on reaction to a tether. Shouldn't be too hard.
Mewtwo is a pain in the ass to gimp, but it's doable. If you catch him with Fair as he's about to teleport horizontally to the edge or stage, then that's bad DI, and assuming he's used his second jump and he's at decent percentage, that should be a gimp. If they don't know their teleport range well or are trying to mix things up by teleporting to the stage, the usual stand at edge and Dsmash can work too, but it's more likely to just reset the edgeguard and rack damage than it is to gimp him. Honestly, you're probably better off just killing him normally, though getting into that scenario is still good for you to rack up damage so you can do just that. Try and read their teleports and throw out a grab or even just a Fair.