I think the most important part of momentum to learn from is the element of disruption. Disrupting whatever strategy your opponent has, whether by walling the threat they have out, removing their hazards, or blocking their attempts to remove your hazards its about controlling the field as it exists at that moment. Very, very few Pokemon can gain momentum if they cannot disrupt the opponent in some way. Most of the Pokemon that can't disript have such insane offensive prowess that to mimic that mold of momentum would not yeild any useful information. Landorus gains momentum by smashing skull A into dirt B. Repeatedly. I'll give a few examples of disruption since it only takes a few real forms. Imperviousness: Most stall teams operate with this as a principle. If a Pokemon can recover more damage than it sustains against the opponent's threat, the opponent must switch. Hippowdon, Skarmory, and Blissey are the most common examples of this, as they have reliable recovery and happily soak up attacks, draining their opponents PP while setting up their strategy. Imperviousness and hazards go hand in hand, as the ability to wall any of an opponents given threats and force switches is the key to maximizing momentum is stall. Reuniclus also exemplifies Imperviousness by combining Magic Guard's immunity to passive damage along with bulky stats and Calm Mind boosting. If you cannot immediately threaten it, it can set up its strategy uninhibited and you must switch before it gets out of hand. Arghonaut provided a different type of imperviousness, and it was the most disruptive Pokemon introuduced in 4th Generation CAP because it completely negated the strategy of stat-boosting. Any time Arghonaut came in on a stat-booster it was basically guaranteed to subvert their strategy. Stat-boosters often maxed out their speed and relied on their stat-booster to muscle through the opponent, and Arghonauts defensive competence rendered that strategy obsolete. It required opponents to play around it all match. Rapid Spin: Obviously the bane of most stall teams, Rapid Spin can turn around anywhere between 1-6 turns of setup in the blink of an eye. Just as important as the move itself is blocking its use, primarily through Ghost typing but also with Protect, or just finishing off a spinner before it can attack. Move Disabling: This one is less common, but takes many forms such as the concept namer Disable, Encore, Taunt, Torment, and Imprison. Disabling that one attack that is effective against that Pokemon can put your opponent in the same situation as imperviousness above. Status: Status has obvious disruptive qualities against most Pokemon, but each status is more specific as to what it disrupts. Burn doesn't disrupt many walls to the extent Toxic does, and Paralysis matters little unless it activates on the healing turn. It's also the most negated form of disruption. Attract and Confusion are similar and less well defended against, but their inconsistency is troubling. Dusk's note about threatening an opponent is also important. Just disrupting an opponent is not enough, once in your disruptive Pokemon must also be able to pose a credible enough threat on its own. Otherwise the only thing it can fall back on is its own imperviousness, and that's a losing strategy in heavily offensive metagames like Generations 4 and 5.