Shadow Fiend Mek Builds...

Shadow Fiend is a hero i've seen who has a pretty varied item build. I've Euls Sfs, Manta SFs, Midas SFs and so on, but the main item I've seen on Shadow Fiend that I'm curious about is Mekansm. Why mek on a hero like Shadow Fiend? Can someone enlighten me on why mek is so popular on Shadow Fiend?

Mek gives a lot of tankyness midgame and has a easy build up. SF really doesn't lack dmg in most cases so some survivability is pretty good.
If you don't go for teamfights though a euls or manta might be better to get pickoffs or splitpush.

The items really depend on what's the gameplan.

Generally mid heroes possessing considerable nukes opt for a mek to boost survivability while simultaneously easing the burden of supports.

SF can get it whilst it's still hugely relevent (Supports going for it, unless it's like an Io, or a support that can flash farm generally get the item late enough that it's primary usage falls off, so it's not a support item as much as a pushing/team-fight item). It makes him much more tanky, and he's one of the heroes in the game that doesn't lack for right-click damage early due to Necromastery. Thus why one way or another you see him go utility first.

So it drastically increases the heroes ability to perform early - mid game, without compromising his damage out put. It's essentially a great item pick up when you want to group up and fight/push early, comapred to the Eul's slight more emphasis on pick-offs.

For the same reason you buy mek on Viper, Razor, Necrophos, Bristleback, or pretty much every mek core ever : to push.

In the current meta, competitive games last about 25-30 minutes in average. So they're essentially reduced to "get an early advantage, but a Mekansm, group up, and push". SF is a really good pusher because he two-shots creep waves.

Besides the mana cost of mek is essentially offset by SF's rather large mana pool as well as buying Eye of Skadi afterwards.

He can get one in 8 minutes in the mid lane and start pushing with his team. Before 15 mins you can pretty much nullify most of the damage your team takes in a fight with a Mek, and it just fits with the playstyles people are using right now where you start bringing fights to people early on and taking towers.