Positioning an enemy to set up G-mode from a heated room requires precise Energy management.
With slightly too much Energy, Samus can take damage then use X-Ray until her i-frames expire to immediately be able to take damage again.
While G-mode provides heat protection (sometimes referred to as 'artificial Varia'), entering G-mode in a heated room is risky, as a fail will likely result in death if Samus had only 4 Reserve Energy.
Exiting G-mode while in a heated environment will remove Samus' artificial heat protection; luring and killing an enemy near the door to collect its drop with a pause abuse is possible.
See also: Tech Page