I haven’t been too happy with my attempts to emulate a Mellotron. (Might be worth a shot using TapeEcho). But it’s a task for several H9s (or realistically, a VST sampler/synth). Currently, you’d have to ‘build’ the source (flutes; strings; chorale, etc.), figure in the soft attack & 8-second tape spool limit, tape wow & flutter …
https://www.eventideaudio.com/comment/11152#comment-11152
As for the hold function, I have an EHX Freeze and SuperEgo + here. You can’t capture ALL of the effects in the SE+, but the H9 can cover most of it (and then some. Unique approaches.). I’ve posted at least a half-dozen threads about this on this forum. Here’s one:
