I realized today that this post, at least in comparison to the other posts I have been making, will be shorter than the other guides, simply because there isn't much content left to discuss. To make up for this, though, I have spent a pretty decent amount of time gaming, recording, compressing, and uploading a poppy game (not really that serious of one, but still a game nonetheless). It is in the upload stages now and I will have them for you shortly, so don't get upset! New videos are on the way! EDIT: Screw this, you guys deserve a video because this post is so small. It just came up.
Anyway, for Poppy Masteries, I go a 9/0/21 build. In the offensive tree, I grab 3 points into Archmage's Savvy and 1 into Deadliness. Although these could be swapped, I just don't like relying on lucky crits.
Rather than type it out, there it is for your pleasure. I grab greed and regen talents because, well, that is essentially (with philosopher stones) how I keep myself viable by countering harassment hard and producing gold no matter what. Improved movement speed plays along with the I get in and out aspect of my gameplay and reducing my summoner spells makes it so I can ignite that much more frequently.
Late game play with poppy (after you get your Death Fire Grasp) can be a bit of everything. Your team may prefer for you to throw your life away to kill their fed carry. You may simply use your presence to deter the enemy team from engaging, hell, you may even dedicate your DFG to knocking down an over extended tank, as well as push them deeper into your team with Heroic Charge (unless it is Amumu <.<). The important thing is to make sure you get your ult off and put someone down, and typically I focus support or a carry. If they have a Soraka, you are the best chance to put the bitch in her place. The one shortfall of your late game play is that while you aren't as weak as, say, a Karthus at pushing in towers, you aren't some back door god either. My advice is to stick with the team at all times unless a situation calls for it, and be ready to blow everything to crush one champion. If you live with barely any life, well, hang around because with those phil stones, you should regen enough life to possibly save one of your allies with a heroic charge, or something to that effect. Oh, and as always, try to let your carries continue to farm. If it is you versus them for farming creeps, let them take it. They WILL scale much better for damage than you will.