Perhaps the opposite of reaction based teams such as hyperbloom are mono-element teams, usually consisting of only one to two elements. Mono teams have been the subject of many meme videos, featuring mono anemo and mono geo teams clearing abyss.

Mono teams are also the bane/antithesis of USA media, who like to sell the propaganda that you need reactions to do damage. But that's not necessarily true. You do not need to vape or spread every hit in order to deal high damage. Anemo, geo, physical units can deal high damage just by having higher scalings rather than doing multiplicative/additive reactions.

Some classical examples of units that can be played in mono teams include: Xiao, Itto, Eula, Scaramouche. Xiao can be played in mono anemo or 3 anemo + Bennett. Itto can fully be played in mono geo (in fact his support Gorou fully encourages mono geo). Like Xiao, Scaramouche can also be played mono-anemo, but benefits from having other elements via his passive (giving buffs depending on different elements absorbed by E) and can even work in dendro hyperbloom taser teams. Technically, Eula has superconduct, but she can still be played in cryo-electro only mono teams.

There are also mono electro teams such as Raiden-Yae-Kujou-Anemo vv/Bennett. Although Cyno can also be played mono, he benefits more from quicken and hyperbloom, whereas Raiden does not necessarily need reactions. Some suggest that Dehya can also be played in mono-pyro comps (3 pyro + anemo vv). Also, although Ayaka technically wants freeze (cryo, hydro, anemo), she is a bit similar to the above characters as she relies more on high scalings than amplifying reactions (the fact that Ayaka is not really used for melt is why an additive buffer like Shenhe was introduced to complement Ayaka).

But then one can do mono quicken teams consisting of 3 dendro + one electro (e.g. Alhaitham, Nahida, Yaoyao, Raiden). So what counts as a 'mono' team? Is it about the number of elements? Is it about not using amplifying reactions? Depending on how mono is defined, it can actually be a very general class of teams or something extremely niche. USA media likes to make mono sound like something very niche, but all the above examples point to how general a 'mono' comp can be.

If you choose a very narrow definition of mono, saying it means you must have 4 characters of the same element in a team, then perhaps the only viable mono teams are anemo and geo hypercarry mono teams (Xiao, Itto). Everybody else besides anemo and geo would benefit from either superconduct or swirl (anemo vv) reactions for res shred.

Perhaps one example of a broad definition of a mono team is a team that uses at most 2 elements. This would include all the above examples except the Ayaka freeze team. Another example definition would be a team that does not rely on amplifying reactions (melt, vape, quicken) or bloom/burgeon/hyperbloom, but instead high scalings. So this would include the Ayaka freeze example, but might be a bit too general as it allows for 4 different elements on the team (e.g. Xiao Yelan Bennett Morax), which does not seem mono at all.

There are certain artifact sets that can adapt to how mono/diverse a team is or give buffs for mono teams. These include the Gilded set (more atk for mono teams), Thundersoother, Lavawalker, etc. As of version 3 there is no equivalent of a thundersoother/lavawalker for hydro or cryo.

The opposite of such mono effects are Nahida, Yelan, or Yun Jin's talents, which buff the characters based on team diversity.

Lyney is a new character that can be played mono pyro. Technically all pyro units can be played mono pyro. The difference is that Lyney's optimal team may actually be mono pyro and that he is specifically designed for that playstyle.