Burning tree emissary and bloodrush

[Empathie]

Can I use the floating mana durning the battle step or does it dissapear when going into the battle step?

[Keyeto]

It will have disappeared by then, unfortunately. Here's your ruling:

500.4. When a step or phase ends, any unused mana left in a player's mana pool empties. This turn-based action doesn't use the stack.

RESOLVED

[Deathstorm]

The mana disappears when you enter your combat phase unless its green mana and you have  {Omnath, Locus of Mana} then you can float mana

[Empathie]

Thanks