I also wrote up a bunch of my favourite plugins in the context of that video, might as well share that too, it was a message to someone in case it reads a bit weirdly lol. Put it in the hidden block below as it’s long and I don’t want to ruin the thread readability!
My plug-in recommendations
Hosts
AUM - already talked about this, it’s the best way to jam with plugins on iOS. Some things could be improved (e.g. I think you could easily fit more on one screen) but it’s great overall.
ApeMatrix - this kind of does the same as AUM but with a strange “matrix” mixer layout. It’s a bit weird but kind of cool once you wrap your head round it, you can do send/return more easily for example. Has a few other tricks like LFO for any parameter of any plugin. Less stable than AUM and definitely not essential but may be interesting if you get into this way of working.
MIDI Sequencers
Rozeta Suite - I think this is pretty essential for working with AUM. You get 8 or so different sequencers ranging from “staple” ones like x0x and Bassline to weird fun ones like a “particle collider simulator” that triggers notes, plus an arp and MIDI LFO.
Fugue Machine - this is the one with the multiple playheads in my video, I think it’s a really elegant implementation of a great idea and is great for taking a simple sequence and making it more interesting, creating evolving arpeggios etc.
Atom Piano Roll - if you need the ability to just program notes into a normal piano roll and then send them to another app, this is the best one I’ve found. Very similar to e.g. Ableton’s piano roll.
Synths/Effects
I generally only buy synths and effects on iOS these days which have an Audio Unit plugin (sometimes you’ll see it referred to as AUv3 on the App Store).
AUM can load synths which don’t have an AUv3 (e.g. Nave - really wish that was Audio Unit as I love it) using something called Inter-App Audio, but you can’t view them in a floating window, it can’t save the state of the synth in your session, and you can only have one instance of the synth – so I find it usually more hassle than it’s worth and go for one which integrates better.
I’ve got quite a lot of iOS synths and effects so I’ll try to pick the ones which I use most or are most interesting, but if there are any specific types you are interested in or whatever I can share more!
Synths
Arturia iSEM - lush analogue emulation that I always enjoy playing with
Audiokit Digital D1 - really nice for pads, based on 80s stuff like the Wavestation I think
Beepstreet Zeeon - another analog synth, I just like the way this one is laid out and sounds, it’s often the one I default to. Same dev also has one called Sunrizer which is a JP8000 emulation if you ever need some 90s vibes 
Spacecraft - as I mentioned, lush weird granular thing. I think you’d like this.
Burns Audio Modal/Resonator/Spectrum - these are AUv3 versions of some of the Mutable Instruments modules. Not beautiful to look at but quite interesting sounds and they’re free!
Moog Model D - simple but sounds so phat! Moog Model 15 is quite cool sounding too though I find dealing with patch cables on an iPad no fun.
iVCS3 - this is an EMS synthi emulation. I have no idea what I’m doing with it but it makes some crazy sounds. Thought you might be interested as it’s such a legendary synth in the experimental world. You can also use parts of it as AUv3 effects on their own which is cool.
Numerical Audio Shockwave - this one’s pretty new. Some kind of crazy FM/PD synthesis. Not dived in too deep but sounds pretty wild.
Drums
This is the one area where I’ve not found that many great AUv3 apps. I’d love something like Machinedrum style but most of the apps out there either don’t sound amazing to my ears or don’t support AUv3.
JimAudio Pure Acid - this is the 303/808/909 one in my video, sounds great if you just want those classic sounds, TBH I use it for most of my drums these days even though I’m not a total x0x obsessive! It’s really fun to use (also fun standalone), sounds great, has its own sequencer and effects, and you can even use it with “multiple outputs” in AUM if you want to apply different processing to different parts.
EG Pulse - I’ve not used this a great deal but seems like a decent drum sampler if you’re into that kind of thing. A bit like Pure Acid, it has its own sequencer and supports multiple outputs. Cos I’m too lazy to curate a sample collection I usually just go for Pure Acid lol.
Bram Bos Ruismaker/Ruismaker FM - I used to use these for drums, they’re pretty fun though I never loved the sound of either. Can get some quite interesting sounds out of them though and I think they’re quite cheap. All this guy’s apps are good, take a look at his stuff on the App Store.
Effects
AudioDamage stuff - all the AudioDamage stuff is great, I actually think I have everything they’ve done and it all sounds excellent and most of it is well designed for iPad. Dubstation is the delay I usually go for but it’s worth looking them up on the App Store and see if anything else takes your fancy as they have loads of effects and it’s all really good, e.g. their Eos reverb is nice.
Eventide Blackhole - my favourite reverb. Eventide have ported quite a few things to iOS now, MangledVerb is also quite cool.
FAC Maxima - I use this if I need a compressor/limiter. I find it hard to get excited about those but sometimes you need one and this does the job lol. All this devs apps have a rep for being really solid.
AAS Objeq - this is quite a cool resonator type thing. Don’t really know how to describe it but it’s a fun effect.
RX950 - this emulates the old Akai sampler AD converters and I find it’s a nice way to add some subtle lo-fi crunch.
Other fun stuff
Drambo - talked about this already, worth noting it works as an an AUv3 so you can build your own synths or effects in it and mix them with others in AUM. Not tried this yet but sounds powerful!
Samplr - this one isn’t AUv3 but I had to mention it as it’s one of my fave apps regardless, you might have already seen it as it’s been around for years.
