Burn tokens are kinda like Gazbag's ice tokens. They sit on a card that has been removed from your deck until you pay a coin per token to remove them in your buy phase. Once a card has no more burn tokens it goes to your discard.
You're going to have to pay me in +1's if you want to use this I'm afraid.
I actually welcome a weaker traveller line, Peasant and Page are absolutely ridiculous cards! Like nobody complains when fan-made durations aren't as strong as Wharf. I think the fact that these have some conditions upon being exchanged makes me want them to be weaker too, otherwise games are just going to be decided on who gets the exchange quickest. We don't need another Urchin, but I'd be fine with another Treasure Map. Anyway, onto the cards themselves.
Dragon Egg: First I have to say, I'm not the biggest fan of travellers in general so sorry if I come across too harsh, I'll try not too. The swing here is real, I'm not sure whether this should give you +$2 and get to exchange if you have a Silver. If you exchange this earlier than your opponent then the faster travellers will give you a huge advantage, the extra $2 will just compound this.
Hatchling: It's a little strange that this works on any non-Copper treasure but Egg only works on Silvers, so that might be a good change for the Egg to tie the cards together more. I like that this gives you a way to clean up the excess Silvers you might pick up and that also is ore of a drawback becasue Silvers are a nice fodder for the Wild Dragon attack. Seems like a decent powerlevel to me, it's probably in between Moneylender and Spice Merchant. I do worry about the Snowballyness of this though, if it's the only thinner available then you're probably forced into an Egg/Silver opening and then once you get your first Hatchling it becomes easier to get more as you're trashing Coppers and then when you're done you cash them in for dragons.
Wild Dragon: The $4+ travellers are stronger than your average card for sure. Donald X. is on record to have said that Fugitive was too good as a regular $4, Warrior is hated enough to be too good for $4, Hero is pretty much a better Explorer and Disciple would be better than Kings Court as a regular supply pile (It's already close but if Discipling Disciples gained more Disciples it'd be insane!!!). Anyway Sacred Grove shows us that +$3 +1 buy with a symmetrical effect is a $5. So this would be an okay regular $5 I suppose? I like your proposed change, it makes it more enticing to keep some Wild Dragons if they don't attack you as well - although I guess if you're drawing your deck then you can get around that anyway.
Trained Dragon: Gaining treasure is nice because hoarding treasure is a thing dragons are famous for. I don't like that this is basically just a powered up Wild Dragon - seems a bit boring? Maybe you should focus on the Hoarding aspect more as Wild Dragon already shows the destructiveness of dragons? Like a permanent duration hoard effect or something? Although you're only using burn tokens on the one card then.
Well there are some things about these that I'm probably never going to like - just the shuffle dependence of travellers in general and how adding stipulations to exchanging makes that worse. I do like a lot of the ideas here though, the line up until Trained Dragon seems pretty well thought through. Trained Dragon is the only real disappointment for me just from a how cool the cards are from reading them point of view, if that makes any sense.
