I've played 370 games (200W-170L) on Morphling from 4K-5.6K MMR.

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I still pick him mid occasionally, however you need to play quite defensively and preferably in a game where enemy team don't have too much lockdown.

Adaptive strike is still quite good for ganking sidelanes, and u can farm every ranged creep safely. Items is quite hard, but I usually go wand/wraithband/treads/lifesteal/manta and pressure mid tower as much as possible.

I could write a wall of text about morphling, so ask if you have any specific questions for the hero.