"Chevalier de Fleur" and "Sorciere de Fleur" were released in both the OCG and TCG as video game promotional cards. Both monsters require weaker Fleurs to speed up summoning them, "Fleur Synchron" and "Necro Fleur", respectively.
The playing style of the Fleur cards focus on bringing out the two powerful trump monsters that then provide either a protection benefit ("Chevalier") or field swarming/field control option ("Sorciere"), backed up by high attack power for a potentially game-winning play.
Both cards work well together in a single Fleur deck, but they equally work very well on their own as a boss monster support option for a mixed deck.
"Sorciere" in particular works very well with Spellcaster-themed decks due to the fact that it can be summoned without relying on "Necro Fleur" at all, but "Chevalier" can work too through the use of "Quickdraw Synchron".
"Sorciere" is also capable of being a fairly consistent OTK deck option when combined "Necro Fleur" that is also capable of performing well if the OTK combination play is blocked or disrupted.
Banish decks and banish tech cards (i.e. "Chaos Sorcerer" and "Caius the Shadow Monarch") in particular can stop both support cards from activating as they must go to the graveyard to trigger their effects, so make sure you prepare for it: "Chaos Hunter" is an excellent defense against this risk.
Both of these boss monster cards are also once per turn or once off use effects, so they must also be carefully managed and protected. "Sorciere" is particularly vulnerable with its 0 DEF and can be destroyed easily if you are careless and is especially at risk against Karakuri decks that often manipulate your monster positioning. Also note that "Solemn Warning" can be successfully chained to the activation of the mandatory Special Summon effect of "Sorciere de Fleur", allowing another way for it to be quickly destroyed.
Finally Bounce decks and bounce tech cards (i.e. Neo-Spacian Grand Mole) can ruin a Fleur deck if focused on the Fleur support cards and boss monster cards, as they can require a high card investment to get to the field, leaving you open to attack.