Castlevania: Order of Ecclesia

Putting the same glyph on both buttons lets you do do a combo of sorts by rapidly pressing Y and X back and forth (it's great for Nitesco). I went through the majority of the game with Vol Falcis and Vol Macir pairs on my A/B glyph sets. Usually complimented by a defense boost from Fortis Fio.

There are some special glyph unions though if you do mix the glyphs up a bit. Nitesco + some weapon does a great glyph union that's essentially the sword union except with a light saber. Umbra and Luminatio have probably the single most powerful attack in the game in their glyph union, though it takes a lot of hearts. I think "some element" + "some weapon" is the standard formula, which you can adjust according to your attribute levels and what the enemies are weak against.

Don't forget to pay a lot of attention to what enemies are weak against (the red markers on their info pages). You don't want to be using slash against robots for example. For bosses, just try out a few elements to see what does the most damage.

Also if you have the Emperor Ring, you can use it to get a LOT out of your potions too (a high potion essentially completely heals you).

Pay attention to attribute weaknesses and don't go through the game just using sword and hammer glyphs. If you are finding a boss hard, try some other elements to see if they do more damage.

Try to 100% maps as early as possible. There will be some obvious parts that you will know you can't get to yet, but otherwise you should check for walls to break. You want to try to rescue all of the villagers and otherwise it could be a pain hunting for any you miss.

If you see a glyph appear while an enemy is attacking, you can steal it from them.

Sometimes you have to wait and let enemies start casting a spell in order to absorb their spell Glyphs.

Don't bother with Super Potions. Rather, when you get an Emperor Ring use that in conjunction with High Potions and food to heal up.

Use the elevator when you get to the top of the lighthouse. You'll know what this means when you get there.

Don't let Goliath corner you, or you will die. You can escape under his big leg stomps.

Unlike virtually every other Castlevania game, strengths/weaknesses actually matter because enemies can survive more than a couple hits now. You still have a couple useless glyphs (when is Torpor ever really useful?), but the elemental glyphs mostly will get a good amount of use along with the hammer/sword/sickle ones. I almost always have a weapon glyph as my main, and an elemental one as a backup.

In addition, backstepping is actually useful now because enemies hurt a lot more than they used to. Get used to not having a ton of cash unless you want to grind. Speaking of which, find a few gold rings, and there are certain areas/enemies you can grind and never need cash again. However, this shouldn't really be needed if you take into account the attributes/backstepping and the fact that food is more economical and useful for healing than potions are (super potions are not worth the cost).

Drop rates on all items, including subquest items, are extremely low. Try to find luck-boosting equipment like the four leaf clover and fool's ring to make them bearable.

If you want to buy recovery items, you will pretty well NEED to find a late-game spell that makes all destroyed objects drop 100 GP, and then go to town on every fixture you can find. Stay away from potions - they cost more than they're worth. Food is the way to go.

Don't forget about your union glyphs. You can recharge your hearts fully every time you visit town, so cut loose with a union every now and then to make life simpler. This goes for minor enemies as well - bosses are not the only ones who pose a threat in this game. Also, this isn't critically important, but the strongest union in the game is any dark glyph combined with any light glyph.

Take notice of suspicious walls. The game loves to hide important items and such behind breakable ones, and there is a sidequest which involves many such hidden rooms that must be done before a certain point in the game to avoid a premature bad ending.

The early bosses are tough, mostly because you don't have much of a Glyph arsenal. The giant skeleton sucks just because even when you're fighting it "correctly," you will still probably take several of its hard hits. Oh, and defeating the crab is good fun.

Don't be afraid to use the Magic Tickets in a pinch; they are cheap and can keep you from losing the few useful items and Glyphs you've found since your last save.

Some chests are hidden and only appear once you press Down; if you see a conspicuous spot, crouch on it and see if a blue chest rises from the ground. They can have some unique and/or useful items in them.