At the start of the next month, before you can do anything, an unnamed ninja pops up from your forces in Terrera, pointing out what she calls ‘a really weird old man over there’. The man who she refers to walks up a moment later, saying that that was a very rude way to refer to him, and besides, he’s just a traveling merchant.
He’s here to sell some particularly rare items to you, including evolution stones and evolution items. This is your chance to make Eevee (if you prefer Flareon, Jolteon, or Vaporeon) and Jigglypuff into much more usable Pokemon, and improve many other Pokemon by evolving them into their final states both now and later on. If you’re shy on money, then this is going to be a lost opportunity, so you’d best hope you’ve been doing a lot of training, mining, and saving so that you have something to spend here- or alternately that he shows up later on when you find you need him again.
All the evolution items the merchant has cost 5000 gold/ryo each, so it’s going to take a fair chunk out of your available resources to buy what you want. Thankfully, the results are well worth it.
In addition to Eevee and Jigglypuff, the only stone-evolving Pokemon you’re likely to have access to so far are Petlil, which needs a Sun Stone, one or two of the elemental monkeys Pansage, Pansear, and Pansoak (most of whom you won’t wind up actually using as their Warriors are often better-suited to other Pokemon), and Kirlia, which a male Warlord can use a Shiny Stone to turn into a Gallade instead of a Gardevoir. It’s safest to make your decision on the evolution items based on what you already have, as there’s no real guarantee as to which Pokemon you’re going to find yourself using the most in the future.
The items he has in equipment and single-use are much less valuable because of simpler things- the single-use items are consumed after one shot, and the equipment is, while sometimes useful, very specialized. One of the equipment items, the Large Sack, is convenient but expensive at 5000 gold/ryo, and is only a one-use item. Given that you’re probably training multiple times in each area, its effect (collect all items left on the field at the end of the battle) simply isn’t worth the price in most cases, and you’re never going to know before hand which cases those are anyways.
Of the non-evolution items he has, the Purple Ponigiri is probably the most useful one, costing a mere 1200 gold and increasing the Energy of a Pokemon to its maximum, improving its performance in battle drastically if it has a low (blue/down arrow) Energy level.