Owlboy is generous with hidden things and unforgiving about explaining them. Because the game has no fast travel and its regions are large, most collectibles are found by deliberate re-sweeps rather than by story progression.
The Tokens of Owl are the game's collectible currency pieces, scattered across every region and usually hidden in the least obvious corner of a room. There are additional tokens behind late-game ability gates, and the count reported by community trackers has varied over the years as patches and platform versions landed - treat any single published total with a grain of salt and verify against the current patch if you are chasing a complete run. What is consistent is that a large majority of tokens are reachable with the full kit, and that a handful require Super Dash or the Auto-Aim accessibility setting to reach at all.
Three ancient relics - including the Artifact of Doom - are the game's spine rather than optional collectibles, and the sky pirate campaign is built around them. Solus is gathering the same relics for his own purposes, which is why the middle of the game feels like a race rather than an inventory checklist.
Enemies drop the colour-coded Ish items described in the gameplay page. Coins are the separate currency, and merchant stalls in the world let you spend them on supplies. Because Ish items are consumables, a merchant with a good stock is worth a detour even on a region you have already cleared.
Owlboy contains a hidden code puzzle, and reviews at launch specifically pointed readers toward the fact that it exists without walking through it. If you are going for a complete run, it is one of the items worth hunting deliberately rather than stumbling into.
Yes - especially now. The 10th anniversary update added Super Dash, which opens small gaps that were previously unreachable, and removed hidden off-screen enemies, which means a couple of classic complaints about the game no longer apply. It also arrives with the game heavily discounted, which is the moment to pick up the base game if you have never played it and then decide whether you want to chase a complete run at full price for the Switch 2 Edition's features.