I was so worried when I saw Lost Remover. Why? Because as I often struggle to avoid, I was thinking in the past. There are many formats where this would have been a good, if not great card. Getting my head into the now, I think it is something almost paradoxical in nature: a good card in a bad format. Sounds like an excuse, right? Read on for a little more depth.
Lost Remover is a normal Trainer. This makes it incredibly easy to play (from a resource standpoint) and you'll still have access to your oh-so-important Supporter usage for the turn. This is important both for capitalizing on the end result or drawing into it in the first place. The card's text states that you may put one Special Energy attached to one of your opponent's Pokemon and send it to the Lost Zone. For a second, forget this specific format and think about it in general terms. First, you're trading a resource that only requires it be in hand to play (Trainer) for something that can normally only be played once per turn (Energy). Special Energy cards rarely make up much of a decks resources, but the decks that do run a lot are even more reliant on them than a normal deck is on Basic Energy cards. Special Energy cards are difficult to recycle under normal circumstances, but even if there is nothing good at it right now there have been such cards in the past, therefore this is a nice but not especially significant bonus; the icing on the cake, as it were.
I will draw attention to the fact that it can hit any of your opponent's Pokemon, as this is quite important: cards that used to be safe to energize on the Bench simply aren't anymore. It has always been dangerous enough for a Pokemon because no format has been entirely lacking in ways to force something on the Bench into the Active slot, and standard operating procedure is to attach general (usually Basic) Energy to a Benched Pokemon first and only attach needed Special Energy cards when it becomes Active. Still, the option to hit the Bench is nice and just adds to hitting the Active. Besides, sometimes you'll want to send an Active to the Bench and by doing this and stripping it of Energy, you greatly inconvenience your opponent: who want's to re-energize a half-KO'd Pokemon? Taking a Prize sooner rather than later is better, but it also isn't always an option.
Now let us begin to filter it through the actual formats. At a serious Modified event, deck space is tight and the impression I get is that you have a lot of speedy, hard hitting decks, or face the dreaded "Trainer Lock" strategy. Most decks run Special Energy, but by the time you are able to tag it with Lost Remover, such decks will have made use of that Energy. Your opponent will already have attacked once with Call Energy, Benched something with Warp Energy, and so on. Even if someone is using Double Colorless Energy, they've still gotten one attack out of it. One of the reasons I haven't done much this format is because as far as I can tell, it is that fast: one attack is usually all that is needed, and for most decks this is an annoyance. So most decks are too fast for the effect to matter, or will block it via a Trainer-lock strategy if they are of a slower set up.
In Limited Play, skip it because the only targets this set are the classic Special Energy versions of Darkness Energy and Metal Energy, which means unless I missed a Common card with a killer combo that uses any Special Energy, most players won't have any Special Energy to remove. Even if you do face off against a Darkness or Metal deck, in this format the Special Energy shouldn't be critical to their set-up because said opponent will know going in they only have one or two copies and lack an easy way to consistently get it into play.
I was tempted to dismiss this for Unlimited play, because we've already got Energy Removal and Super Energy Removal. Why restrict yourself to Special Energy cards when you've got a Trainer that can discard any Energy or any two Energy as long as you discard one of your own Energy cards? Then I remembered Recycle Energy! Unless the Unlimited format has radically shifted, a significant number of rogue and archetypal decks will want to use Recycle Energy, and most decks will be quite low on Basic Energy. In short, if it isn't something like a Rain Dance deck that intentionally abuses Basic Energy cards, Unlimited decks are mostly powered by things like Double Colorless Energy, Double Rainbow Energy, Rainbow Energy, and Recycle Energy. Said decks don't run much Energy to begin with, so while there might only be 12 Energy and four of it end up as Basic Energy, changing over one or two normal Energy Removal to Lost Remover sounds like a safe bet. Against most decks, you won't lose any utility because again, they are running Special Energy cards you can target or Basic Energy cards they can easily recycle and re-attach.
Ratings
Unlimited: 8/10 - Kills Recycle Energy, plus this is the format where reclaiming a discarded Special Energy is easiest. All while losing almost no utility due to standard deck composition. To top it off, most decks will be able to TecH in one in place of an Energy Removal and just use Item Finder to reclaim it if it is worth using again.
Modified: 5.5/10 - I am still tempted to squeeze a single copy into a lot of decks, just because the times when you want it you need it, but it will be a dead draw far too often to run anymore.
Limited: 1.5/10 - If you just need a card to make 39 into 40, it beats an unsupported Evolution.
Summary
I have to emphasize that this format is one of the worst Modified formats for Lost Remover to exist in, and that you should be taking advantage of this time to snag four copies for next format, or in case of a radical shift in the established order. Definitely test it out because reliably removing Special Energy cards looks so good on paper. If you're playing Unlimited, definitely snag a full play set because you really should be including one or two in your default deck build, and might find four useful depending on your local metagame.