interesting items, spells and combat techniques

[ekolis]

Combat techniques that you learn by equipping certain weapons, like in Final Fantasy Tactics Advance. So a great-axe might grant the Cleave ability, and you can use the Cleave ability so long as you are wielding the great-axe. But if you gain enough XP while wielding the great-axe, you learn the ability, so that you can use it even if you are wielding a different weapon.

[Etinarg]

.. spells that would break the routine in roguelikes. I'm mostly concerned with combat, adding some tricks and twists, ways to kill stronger monsters, deception, etc. Something other than the usual scroll of teleport

You could try more occult magic. Like a spell to turn a creature into a potato beetle, and then let the player use a bug spray to kill.

The trick here is to use a two-step approach - first some transofmation or effect that makes the monster vulnerable to an otherwise non-lethal effect, and then use an item to deliver this effect.

Edit:

putting wooden things on fire

This goes beyond basic spells and items, but you could make the environment react to certain spells. If you cast a very powerful fireball, stone will turn to lava, and water into steam. If you cast an acid bolt into a hot area it will turn into poison gas. Cold effect spells will turn water into ice (-> slip, slide), and lava back to stone.

If you have impact based spells they can turn stone to gravel and gravel to sand. If you have movement modifiers, gravel is slower to walk but a tiled stone floor, and sand is even slower to walk. If sand is turned to powder, it can become a problem to breath there and it blocks sight.

Acid will melt stone to mud.

Many RLs let spells affect items (burn, melt, freeze ...) and it might be interesting to extend this to the environment.

[Trystan]

...it might be interesting to extend this to the environment.

Yes. That's a topic that I'm exploring right now and I think affecting the environment allows much more fun and interesting tactics. Not only has it lead to really fun situations that require thinking rather than stat rolling to get out of, but there's a lot of emergent and unexpected gameplay.

In fact, this was almost what I was going to do for my 7DRL: a game where all you can do is alter the environment and try to shape it in a way that makes you win.

[Etinarg]

UnAngband has such a system AFAIK. I heard that it can be quite deadly if monsters breath "unlucky" elements and a room changes into living hell. (water->acidic steam, stone->lava, water+electricy -> extra shock damage)

Room with rock and water + fire ball + acid ball  = suddenly you are in a sauna with no breathable air, acid steam which eats your weapons and armor, and evey second step, puddles of molten rock which burn you and you can see nothing. With safety goggles about two feet more.

If you have furniture that can burn and fires which can spread it becomes more of deathtrap.

I guess people will want fire extinguishers, gas masks, air supplies and rubber coats in such a game. Along with stainless steel blades, and noble metal plated armor. Or fiber-ceramic based equipment, which does not conduct electricity, is not harmed by acid, and does not weaken in heat as quickly as metals do.

A stoneskin spell can be a temporary lifesaver, too.