Mega Man X6/Heart Tanks

Commander Yammark
Requirements: None

After entering the blue cavern, you will find a pit just before a Rescuable Reploid and a Nightmare. Jump down this pit to find the Heart Tank, alongside another two Reploids and a Nightmare.

Ground Scaravich
Requirements: Nothing but luck

The third or fourth totem gate may take you to the level section with the Heart Tank at random chance. You can recognize the section by the fact that it goes entirely on an upward slope. The Heart Tank will be in plain sight towards the end of the section.

Blaze Heatnix
Requirements: Metal Shark Player's nightmare effect, or the Jumper part (found in Blizzard Wolfang's stage) when playing as Zero or the Jumper and Hyper Dash parts (found in Blizzard Wolfang and Rainy Turtloid's stages respectively) when playing as X

After fighting the second Nightmare Snake of the stage and entering the next boss gate, climb all the way to the top to see the Heart Tank slightly obscured by a Rescuable Reploid, next to a Nightmare on an overhang. If Metal Shark Player's nightmare effect is in action, a metal block will be moving up and down to the right. With some careful movement, you may grip the side of the block as it is moving up and dash jump off the side of the block to reach the overhang. This won't require any parts regardless of who you play as. Be prepared to take the Metal Anchor/Rakukojin with you though, as you won't be able to progress much farther down the alternate path past the Heart Tank without it, as another metal block completely blocks the way and can only be destroyed with these one of these powers. You will miss out on the stage's other items in this case. Alternatively, Zero can reach the overhang with the Jumper part and X can reach it with the Hyper Dash and Jumper parts.

Blizzard Wolfang
Requirements: Blaze Heatnix's nightmare effect, in addition to: Blade Armor or Shadow Armor or Zero

If Blaze Heatnix's nightmare effect of falling fire balls is active, there will be an opening in the wall at the end of the very first downward slope in the stage (immediately underneath the Light Capsule's location). You may see the Heart Tank below you, slightly obscured by a Rescuable Reploid next to another Reploid; head to the right and drop down then move back to the left. You should be standing below an opening up into the small enclosure with the two Reploids (destroy any Nightmares you encounter to stop chance of Reploid loss). Use the Blade Armor's vertical mach dash, the Shadow Armor's ceiling stick ability or Zero's double jump to reach the Heart Tank and Reploids.

Rainy Turtloid
Requirements: None; Falcon Armor or Zero's air dash, Blade Armor's mach dash or the Shadow Armor can be used too.

The Heart Tank is located on the second path from the bottom, on the left side, of the final, expansive room before Rainy Turtloid himself. The are spikes on the ceiling and floor right before it. Take a hit from the enemy and use the invulnerability frames to surpass the spikes and claim your reward. You may need to take a death after obtaining it. Alternatively, you can use the Falcon Armor or Zero's air dash or the Blade Armor's mach dash to fly between the spikes or simply use the Shadow Armor to walk over them.

Metal Shark Player
Requirements: None

This Heart Tank is difficult NOT to get. Towards the end of the stage, just before the Nightmare Pressure miniboss and just after 'that' jump which is very awkward to survive without an air dash of some description or invulnerability abuse, the Heart Tank sits at the bottom next to a Reploid. Given the tight timing and necessity to crouch to survive the ceiling crusher, and the conveyor belt moving in the direction of the Heart Tank, it really is a bit challenging to avoid getting this item. If you needed to read this entry to find it, then clearly you are both blind and very good at Metal Shark Player's stage. Congrats.

Shield Sheldon
Requirements: None; Shadow Armor can be used

The Heart Tank sits on a bed of spikes in plain sight past the Light Capsule's location down the stages' alternate path. The alternate path is accessed by deflecting the laser just before Shield Sheldon himself onto the door on the floor. You will have to complete a challenging laser deflection puzzle first before you may reach this bed of spikes. Take a hit from the nearby Nightmare and use the invulnerability frames to obtain it. If you wish, you may also use the Shadow Armor to walk on the spikes to get it.

Infinity Mijinion
Requirements: None

The Heart Tank rests right behind the Light Capsule; to the immediate left of the spawn point in the stage's Nightmare Zone, accessed through the portal after defeating Illumina. Try getting the Heart Tank before the Capsule just for the fun of it.