It's underused, but there's a slight difference between being not useful in the actual metagame, or neither in arena/AI 3-6 for a reason. This card is too crappy even for a Nightmare combo to fill your opponent hand with sh*t.
1, Why does Chimera useless in mono? I rather draw an other monster to rush than 'do nothing' for 7|6, gravity uses momentum without it, anticombosive with Acceleration and Catapult (3 Armagio with Catapult deal 60+2+1 dmg, transformed to Chimera deal only 43) or Otyurg or Salvaging. Gravity has PC and good PC-s, so a shield can't be a matter.
2, Duo-s
-> Anticombosive with mitosis | Adrenaline | Emphatic bond | Green Nymph.
-> Various of combinating possibilities, but SoF is better to hack up the shield than this and burrowing is safer.
-> Rather quanta deny, where it's not needed.
It's just not worth being in a duo.
3, Trio,rainbow
Exponentially not worth.
It's not worth to combinate with any ability creature.
->Unlike Shard golem, a Rewinding makes it 0|0 if it's played again (so actually it kills this card).
-> if the creature on the the first slot is Aflatoxined, the Chimera will die not depending on how much and how big it will be (except if 1 of them is burrowed or immaterial). And alfatoxin is still cheaper than.
-> I don't know if it's a bug, but if I draw Chimera with SoBr it's automatically plays it and takes an other in hand (even if I don't want to or the field is empty).
Gravity pull kills it (the fun that the card automatically has a pull) against an other rush easily.