Once the Roar chain starts, there is no stopping him. While Roar can be prevented through Taunt, Riolu can simply Protect+Copycat the Taunt back at the user. Roar + Prankster Copycat means that any Pokemon without priority (non-existent in this meta) or Protect will be phazed out before they can even move. This makes Toxic damage build up quickly. Sub is an alternative over Protect to make damage build up faster, but you can no longer Prankster Copycat status moves such as Taunt effectively. Hidden Power Poison is in case you get Taunted and the IVs provide a HP Poison of BP 30
Also, I theorymonned the following set
Deoxys-A @ Iapapa Berry / Berserk Gene (when will this get released?)
EVs: 252 Atk / 252 Spe
IVs: 0 HP / 0 Def / 0SDef
-Skill Swap / Taunt
-Recycle / Taunt
-Knock Off / Fling
This is only in theory, mind you. Sub down to Iapapa range, get confused and hope you hit yourself. You easily KO yourself even after the recovery. Recycle is to retrieve the berry after it is eaten so you can confuse yourself multiple times. If Berserk Gene was released, Deoxys-A actually OHKOs itself of it hits itself, that shows how, er, amazing its defenses are. Fling if you already used your berry / gene and didn't opt for Recycle. No damage is good news for a Pokemon with an insane attack stat.
I like the PerishTrapping Smeargle set but I'd go with Whirlwind + Knock Off and Toxic Orb, so in case you fail to get off Perish Song you can still outstall yourself with Toxic Orb.
I ran a very similar Riolu, and while it does its job well, it doesn't stop the opponent from doing their job - Black Sludge and status will continue to lower the opponent's health after you Roar out a new Pokemon.
If I do this, the set has absolutely no way of avoiding Taunt, which is the entire point of Magic Guard / Mental Herb. The entire point is to Perish Trap yourself, and the extra bulk + Ingrain is there to ensure that you pull it off.
It might be a better idea to use Switcheroo, since the only Pokemon with access to both Imprison and Switcheroo is Smeargle, whereas Imprison + Trick is quite common. That said, that looks like one hell of a set to face down. Perhaps Substitute would be better over Thunder Wave though so you can die faster and leave the Thunder Waving to another Pokemon...
I believe a frail pokemon with limber could potentially be useful, to absorb t-waves and prevent itself from being t-waved. Or maybe (if magic bounce is common) you can run entry hazards and use magic bounce to bounce them back to yourself. Just theorymonning, as I haven't played this metagame yet.
Run max speed, min physical attack. Start by using Sketch on nothing; it fails. Then Struggle to death. This achieves a self-KO in just four turns (if your HP is divisible by 4), faster than most of the other methods I've seen. The great thing about the set is that Taunting it doesn't hurt it at all, unless you're Taunted on the switch.
I don't see why last Last Resort should be banned since it is not OP and also is a niche move, after all it does force you to not use all your moves. Synchronoise is something completely different though, it is also a niche move that is situational, but sometimes it might be a bit rare for it to even hit. Definitely suspected for banning. Snatch also might see some competitive use since, unlike standard play, most moves are easily taken advantage of.
Azurill with toxic orb, protect (to take thunder waves) splash, substitute and bubble seems like it would work
Run max speed, min physical attack. Start by using Sketch on nothing; it fails. Then Struggle to death. This achieves a self-KO in just four turns (if your HP is divisible by 4), faster than most of the other methods I've seen. The great thing about that set is that Taunting it doesn't hurt it at all, unless you're Taunted on the switch.
This set is ingenious and should always be considered for a team slot, I can see this set having a few problems too, since some pokemon can kill themselves faster. this is definitely a set to prepare for.
Skill Swap Alakazam can guarantee a win in the last turn, But it can be countered by other means, Such as KO'ing it on purpose, or suiciding a pokemon that can kill itself no matter what (Even with Magic Guard).
Alakazam is definitely one of the most powerful threats and should definitely be suspected for a ban.
Use perish song, then roar to phase opponent, then baton pass to something on your team to kill it. Scratch is the most worthless attacking move I could think of besides rapid spin, which you don't want for obvious reasons.