I tried playing this casually and made it all the way to round 12 however I had very view items and was getting destroyed repeatedly. I searched and found this video which of course isn't mine, but was extremely useful for finding useful items (
sword upgrade, shields,
herbs) and only took maybe over an hour.
Enemy encounters are random, but the items they drop for the most part are not. The only time my items differed from the video were sometimes I got a compass instead of a shield (not a big deal, I had 6 shields by the time I was finished). If you follow that path, you should end up getting the sword upgrade which will make the later stages way easier especially the end of the round Dragon fights.
Items are used by selecting them while the game is paused, and then pressing down and jump.
I saved up my chalices (I believe I had 4) for the end. Using them mid-stage skips the level allowing me do skip half of round 12.
It may go without saying, but try to keep your stamina high by the end of the stages so you get the max EXP bonus. Eventually you get Stamina bar upgrades based on high levels of EXP.
Running, double jumping and downward thrusts!These are important too. Running is somewhat of a double tap in the direction you're going, don't double tap too quickly or it won't always work. Double jumping timing is really weird, practice it some to get used to it before maneuvering tricky jumps to higher ledges. The downward and air thrusts (pressing and holding down and the attack button while in air) are very helpful for enemy encounters, some will go down in one hit.
Enemies, Boss Encounters, and RewindMake use of the rewind feature for enemy encounters. The enemies that show up are all random, so if an enemy is giving you a rough time simply rewind to fight someone else. Personally I liked fighting the Bishops whose only real threat is that they remove a shield if they hit you (easily avoided with a high jump and downward thrust) and the wizards that whirl swords in the air (they miss a lot of the time and were easy to beat). One other thing, there's a crappy game mechanic can occur that allows you to get juggled in the air defenselessly by some enemy attacks like dragon fire for example; remedy this with rewind.
It was also frustrating when a random enemy would appear and knock you off a rope, once again rewinding can basically swap out a different more manageable enemy in those cases.