^ There's not so much a disadvantage in tactics variety in a 40 card deck if you put it together right. There's actualy more variation, because you've got a lot of playable singletons and anything you replace opens up your options and interactions with what's already there. It's just that your draws are more consistent and you can play more different cards without gimping yourself. Sixty card decks usually just pile on consistency aimed at a specific strat, the best 40 card decks are more toolboxy by nature.
Fewer "dead cards" on average too if you know how to build them. And if you want even more variety - whishes, no joke. Just always have a decent suite of agressive creatures while you whish for your bomb/solution of choice. Learning to draft ODY/TOR/JUD is a skill anyone should develop, tbh, that's a hell of a block ^^
And my disdain of megrim if someone finds it offensive - that thing lures newbies into a wrong mindset, it looks like a discard card, but it isn't, there's no such thing as an effective discard focused strategy. That thing only kills people with "draw 7 descard 7" power cards like
Wheel of Fortune but even then it's suboptimal. Discard is always utility/sideboard, and the best ones in my experience are:
Hymn to Tourach (hard to argue with that) - for mono black, or supremely flexible mana bases
Stupor - A bit weaker, a bit slower, but still sorta does it's job in the right deck
Thoughtseize - obv.
Duress - to have in the sideboard if you have removal in the main deck and the other guy is immune to it
Mind Sludge - one off in mono black controll where you can tutor it up
Last Rites - best one there is but you gotta be playing the right deck, but it can effectively take out the entire hand from the other guy, while you put reanimation targets into the graveyard or just enable madness/hellbent/threshold (It's like armageddon, but with cards)
Cabal Therapy - but that for when you REALLY know a metagame. Still you can go places with that.
There's other forms and more playable ones than those (like cratures which temporarily take cards out of your the other guy's hand), but in general, those are the best. Maybe
Persecute, but it's kinda easy to miss with that thing and you can't build around it as well as you can around
Last Rites in my experience.
Otherwise,
Slavering Nulls + a bunch of efficient R/B removal (but really efficient, like
Firebolt,
Seal of Fire,
Vendetta etc.), as it deals damage and causes discard.
It's more of an utility strat which you shouldn't overdo, as there's just too many situations where a discard card is a dead draw. If it doesn't do anything but cause discard, apart from the ones listed above, it's probably not something you'd want in your deck (or if you're playing it you'd probably be better off upgrading it to one of those depending on your deck).