Retrained Black Brachios

[Toffee.]

Once per turn: You can target 1 Attack Position monster on the field; change that target to face-up Defense Position. This card inflicts piercing damage. If this card is Normal Summoned: You can Increase the ATK of all Dinosaur-Type monsters you currently control by 300, until the Opponent's End Phase.

Basically the reason for why the change-to-defense is now once per turn, is mostly because it lets it retain it's original gimmick, but can still be used, regardless of how it hits the field, and for however long it stays in play. Piercing is more or less an incentive for you to want to keep this monster out, and to make it more of a threat, on the grounds that it can change things to Defense, and proceed to run it over; Assuming it lower DEF. The temporary ATK boost is mostly just for showing off and/or making it and any other Dinosaurs you might control, do more damage for the duration of the whole effect, and make them more intimidating in the Battle Phase.

[Mdoraz]

I think the effect looks fine, except with the last ATK boost effect.  With brachios at 1800, its a normal summon monster with 2100 attack, which is overpowered. I would lower Brachios's ATK to at most 1700, so that it's boosted to 2000, which is somewhat reasonable

[Toffee.]

With brachios at 1800, its a normal summon monster with 2100 attack, which is overpowered.

Cyber Dragon says hi
Photon Thrasher says hi
etc
etc

The boost is only until the End Phase of the Opponent's turn. It's not permanent.

[Trebuchet MS]

It's an okay card. Juggling opponent's big beaters to Defense Position and exploiting their weaker stat (if possible) allows it to take down a fair number of monsters. 2100 ATK for the first turn where it can attack helps enable it and its fellow Dinos to push for damage for that turn. Piercing is pretty much icing on the cake in the off-chance a battle-immune monster appears. Not stupidly strong, yet not laughably weak.