Switching game modes can be fun when it's done judiciously, but it can be a hard rhythm to get right. By game "mode", I'm referring to a design technique that creates a parallel game state that replaces the established mechanics of a game with new mechanics until some condition is met. On the tabletop, many games do it transparently so you're hardly even aware that the game mode has shifted, and it just feels like the normal everyday turn order. When it's done poorly, it feels like 2 or more games got smashed together in the hope that players can endure the disruption.
I became aware of this technique through tabletop roleplaying games, but it can exist in almost any kind of game. The concept of a "minigame" is a subset of game modes, so it's especially common in video games, which often switch game modes for tasks like picking locks, or disarming a trap or bomb, and so on. It's different from a game phase however, which indicates that there are different parts of a player's turn during which specific actions can be taken.
Minigames are probably the easiest mode switch to justify. A minigame frequently exists only under the auspices that a specific activity is so specialised that it requires focus to the detriment of everything else going on. Of course you'd have to play a minigame in Mansions of Madness to crack a safe or to decode an occult manuscript.f It's easy to believe that in character, you'd have to block out the activity around you and concentrate on getting the puzzle correct. There's no room for mistakes, and it's not something you can do as an afterthought.
Just as importantly though, you'd expect the game mechanics to be drastically different from the rest of the game. We all understand that picking a lock, or decoding ancient text, or piecing together torn photographs or documents require notably different skills than walking around a mansion interviewing suspects. It makes more sense for there to be a minigame with new mechanics than for a specialised task to be the same as shaking hands and engaging in conversation.
Some games use different modes to signal a global phase of the game. Betrayal at House on the Hill switches its game mode drastically, but only once, and in such a way that it feels momentous. At some point during the game, one player becomes the traitor and starts actively playing against the other players. It's admittedly abrupt at first, but after playing it once you get used to the rhythm. When it happens, all players understand that the nature of the game has changed. It's no longer a cooperative game, and the endgame has begun.
In 10th edition Warhammer 40,000, there's a sneaky game mode shift just within a single phase of a turn. On your turn, only your army makes attack rolls during the shooting phase. But during the close combat phase, every miniature, regardless of which army it belongs to, involved in melee makes an attack roll. This represents how lethal melee combat can be. While you may be able to take a shot at someone from across a battlefield without immediate return fire (because your enemy has to locate you first), in melee your enemy can easily and immediately fight back.
On paper, it might seem inconsistent. However regimented the Warhammer 40,000 turn structure is, both players are constantly engaged during the game. Even when it's not your turn, you still must roll saves to determine whether hits get through your armour, and you may have overwatch actions, and so on. The game mode changes for a phase of a turn, but it makes that change for both players on every turn. It's part of the rhythm of the round.
A different game mode can signal (or create, in some cases) a change in how you perceive the passage of game time. Changing from exploration mode to combat mode in Dnd is theoretically switching to "slow motion." Every swing of your weapon that takes just up to 6 seconds in game time suddenly takes several minutes in real time. It's meant to mimic the way thoughts race and reflexes take control during moments of stress.
It is, however, hard to ignore the real effect of Dnd combat on player perception of game time. A 30-second battle in game time can have a real time duration of 2 hours or more, so many players feel like several game days have passed by the end of a minor skirmish. The way humans engage with fiction is surprising though, and we often forget the details of a battle that happened last week, and remember just the 30-second highlights. Changing modes in Dnd is inelegant when it happens, but largely effective in retrospect.
In a venerable game like Dungeons & Dragons the awkward change from one mode to another is often mitigated by the players. Rolling for initiative is almost a ritual that's developed over the decades of Dnd play. For many players, it's the signal for players to sit up straight, focus, and think tactically. Often a roll for initiative means the battle mat gets laid out on the table, the miniatures get taken out of their boxes, terrain gets set up. It is definitively a different game, but one of the 2 games most players have agreed to play. This is the rhythm of Dnd, and I think it only gets away with its tonal shift because it's a really old game that has evolved from being just a subsystem to connect wargame scenarios into its own game system.
Many (or maybe most) players of actual wargames don't think of the time between games as an official part of the game. Wargamers perform administrative and hobby work between battles, but they don't spend time exploring the land, entering every tavern in a town, turning over every stone on the path to next battlefield, or having conversations with an NPC for an hour. The only structured game mode in most wargames is the battle itself (the combat mode of an RPG).
Tabletop RPGs aren't dissimilar, except that they have rules around the lack of structure. After combat in most RPGs, the game abandons any notion of turn order or actions or turn phases. The difference is that in an RPG, the players don't leave the table after they've pack away their miniatures. They just keep playing the game. The strength of that system is that they get to experience how and why the next battle occurs. The weakness is that they have to spend real time finding their next battle. There's no fast-forwarding through the uneventful parts, or jumping over obligatory hurdles just to get to a battlefield that's obviously inevitable. In many ways, a wargame is the most efficient way to play with toy soldiers, and accordingly its secondary game mode is entirely optional. If you want to develop the story of why 2 armies have met on a battlefield, then you can do that in your spare time. If you don't care about the details and just want the 2 armies to settle their differences, then you can put your trust in the imaginary politicians of the game world.
One risk of most game modes is that players become dependent on a mode to support suspension of disbelief. Simply put, if the game mode didn't change then the fiction didn't "really" happen.
I don't know of many Dnd players who would be comfortable skipping over combat on the assumption that the player characters would definitely be the victors. There's always the chance that a group of seemingly everyday street thugs could catch heroes on a bad day. It only takes a few bad rolls from a player and a few good rolls from the game master for serious damage to be done. Even without massive damage, combat often costs resources in the form of potions or a short rest or similar. When you forego changing the game mode that has come to define a fictional event, the players don't form memories of the event. It's like the combat never happened, even when there's agreement around the table that there's no point in playing it out.
If a minigame is synonymous with picking a lock in game, then skipping the minigame means that the lock just wasn't picked. The player may rationally understand that skipping the minigame is shorthand that the game character has gotten so good at picking locks that it's functionally pointless to force the player to go through the steps of a minigame, but the player is nevertheless robbed of the fictional memory.
Oathsworn: Into the Deepwood changes game mode into a miniature wargame (such as it is) just for boss battles. It's an abrupt and wholesale change of play style that uses a completely different rule set to the rest of the game. On paper, it's no different from a wargame that bridges campaigns with a story, or an RPG that connects battles with exploration and social interaction. However, a boss battle is only a subset of all the combat that occurs in the game.
For combat encounters in the story mode of the game, you use the narrative rules. There's no battle mat, no miniatures, no special abilities, no action point tracking. You draw some cards or roll some dice to determine the result of the combat, and then continue with the story. A boss battle is inevitable though, and it changes the game mode to a miniature wargame. Players must learn and then recall a different set of algorithms. It's a mental load, to say nothing of a social transition. One minute you're sitting around in real life contemplating how to navigate interesting conversations and intriguing mysteries, and then suddenly you're expected to sit up straight and strategise for fear of losing your player character.
Different game modes can be used effectively to signal a change in focus, concentration, importance, and danger. When done well, they add variety to the game experience and help form powerful fictional memories. When done poorly, they tax players with new rules, more assets to manage, and a disruption to the mood of a game group's social interactions.