Combining Abilities is a game mechanic that lets the player combine two or more of their abilities together to perform a new ability, with different results based on which abilities were used. In my ideal implementation of this mechanic, the player has a set of simple but diverse abilities that each have a basic effect on their own, but when combined have advanced, unique effects.
I like this mechanic for the experimentation aspect, especially when you can learn the general rules of what result a given combination will produce, but you still want to try in case you get something unexpected.
In this game, Kirby can take enemy powers as usual, but can also combine two abilities to create a new one. It's fun to experiment with the variety of powers available since each duo is unique, including using two of the same power. However, it's not a simple matter of just thinking of each pair of powers, since not every enemy type appears in each area.
Having every combination result in a unique ability is really cool but makes it hard to predict what kind of ability you'll get from an unknown duo. In development though, it's tough to commit to making a full set of animations and effects for every possible combination.
Magick lets the player combine 8 elements into a variety of spells, using up to 5 components to a spell. There are no limits on casting - you can go nuts and use your spells as much as you want. In addition, you can use each spell in a variety of ways:
There is a logical result to each combination of elements. For example, if Rock is included, the spell will be a rock-based projectile with the other elements included applying their effect where the rock lands. Using the Wall element will turn a spell from an attack launched to an elemental barrier (or a simple force field, if no other element is included).
It's easy to experiment with various combinations, since the game doesn't restrict how many spells you can cast and how often. You can learn the logic behind it, but there is still room for surprising results, since there are so many possible combinations, as well as variations on how to cast the spells.
In Transistor, over the course of the game you collect about 20 abilities (called "functions") to use in combat. Active abilities have two slots to fill with other abilities (from the same pool). Placing abilities in these slots will give primary ability the secondary effects of the chosen sub-abilities, or enhance it in some other way. The abilities produced from combinations aren't that interesting since they only really add effects together in a simple manner. For example, applying the stunning attack to any other attack generally causes that other attack to stun. The only experimenting worth doing is finding out which combinations are effective in combat.
What really damages the experimentation aspect is that while browsing abilities to combine, you see a description of what would happen by adding the two abilities together. There's no mystery, it just tells you what you going to get. However, you still want to experiment with various combinations to see what is most effective against the enemies.
You collect "glyphs" which are physical or magical attacks. You can equip two at once, allowing for attacking with one than the other, or also using them together as a "union glyph". The implementation is really lacking though, as the vast majority of combinations give you a "dud" effect. For the most part, only combing weapons with themselves, weapons with elemental attacks, or elemental attacks with themselves create real results. While playing there were many occasions when I thought I was about to create a cool combination, only to see the dud effect instead.
It's like Magicka's system, but instead of hitting keys, you draw symbols, and the more accurate your drawing, the more powerful the spell. Kinda neat! But you're severly limited on mana and can only cast a few spells at a time, before having to wait for your mana to regenerate. You also have to play an RTS using a touch screen, which isn't much fun.
You can use Techs (Techniques) in battle. These attacks do more damage than regular attacks. There are also duo techs that involve two characters both using their techs simultaneously for a greater effect, and triple techs that use three characters techs. It's really great to unlock a new duo tech, check out the cool animation, and work this new ability into your gameplan.
You create gems of various types, which get placed into towers so they can fire projectiles at enemies. Each type provides a different benefit, such as poisoning the enemies, splashing damage to other nearby enemies, or collecting mana (used to buy new gems) on each hit. Combining gems increases their stats, and combining different types of gems gives them the benefits of each type used. Multi-type gems have enhanced stats for damage, fire rate, and range but weakened ability power, wheras single type gems are focused on their ability.
There isn't a great deal of experimenting to see what kind of results show up from combinations. Instead you try different types of gems in various layouts to try to improve your defenses. The more exciting part is hoping you do well enough to be able to build up a really powerful gem.
Combining abilities is great when done well, but the game has to feature it as a main mechanic, possibly at the expense of other aspects of the game.
This article is focused on my personal ideal of the Combining Abilities mechanic: a unique result from each combination, and a complex but learnable set of rules, along with game design that allows for and encourages experimentation. It's not a criticism of these games, they're all great except for Lost Magic.