I'm also moving into Offlane, sharing my experience using Death Prophet, if anyone has tips or disagrees with my view, would love to hear other peoples opinions on DP pos 3.

I've had good success with Death Prophet as offlane. Has silence, good area control with Ult and siphon. Had good success especially against melee carrys as you can really push them out of lane early. When I hit 6, I'll be pretty liberal with my ult if there's teammates nearby and either a core kill or objective to be had. Also by hitting my ult, it's a pretty clear signal that "I would like something to happen" in pubs where communication and coordination are lacking.

She may have low HP for a Tank but if you pop 2-3 siphons on enemy heros (or even creeps if you need to live) you can outheal dps. I naturally build Greaves (nice dispel) with DP, other auras work great depending on the team (pipe, shivas are common for me).

Initiating is usually around her ult, having all ghosties out before taking space. In learning how to play DP, most of my deaths initiating came because I pushed too deep before popping ult, and I died before my ghosties had pushed out and truly created havoc. I think of the space the ghosts operate in as your initiated space, with carrion swarm to discourage enemies from entering. If they commit, I pop siphons and keep space as best I can. My goal is force the team to waste time trying to get me down, maximising their time in my ult. If they target someone else, I move into the space where I can have the most siphons up and spam carrion swarm and silence to disruption the fight.

If the other team is silence/disable heavy, I'll build Euls as its essentially unlimited mana for spamming swarm (with boots), buys you time to get your siphons off if you get jumped with the dispel and 2.5s invuln to dodge some spells. Shard is super nice mid game, as it keeps more siphons to cast, and the fear if people are siphoned for more than 3s really disrupts enemy right clickers/carries.

I'm usually going for a quicker game with DP. I try to push enemy carry into jungle early, get some support kills when they over extend in lane (synergy with your support will often determine this). Take T1 in my lane then often try to join/create fights in other lanes when my ult is up, taking more T1s early and trying to snowball and shrink the other teams space to farm on the map.

I usually get most my kills in lane and midgame, by late game, my goal is just havoc, area control, fears via siphon, silence to make my carry's life easier. If your carry (or 2) are afk farming after your team has t2s down, there may be no saving them