Mega Man X6/Energy Tanks

Health Sub Tanks
Function: When you pick up health while X is already at full health, it will fill up these health Sub Tanks. Use them any time to increase your health; handy in boss battles.

Sub Tank 1
Location: Commander Yammark's stage

Requirements: Jumper part (found in Blizzard Wolfang's stage), Hyper Dash part (found in Rainy Turtloid's stage), Speedster part (found in Ground Scaravich's stage) or Ultimate Armor

Early in the stage, you will encounter a large room inside the cavern which you approach from the right and must go down to progress. The Sub Tank is located on an overhang, along with a Rescuable Reploid (who has the Life Recover part; essentially a free full Sub Tank in itself) in the top left corner of the cavern. Dash jump from the upper ledge on the right side with either the Jumper, Hyper Dash or Speedster parts, or a combination of the three, to reach the overhang and obtain two miracles in life recovery. Alternatively, the Ultimate Armor's Giga Attack can allow you to reach the overhang from the other side with ease.

Sub Tank 2
Location: Blaze Heatnix's stage

Requirements: Metal Shark Player's nightmare effect and Metal Anchor/Rakukojin, 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

The Sub Tank is located in plain, easily obtainable sight in the stage's Nightmare Zone, on the right of the ascent. The Zone is accessed from the portal at the end of the main stage's alternate path. The alternate path is accessed after fighting the second Nightmare Snake of the stage and entering the next boss gate. Climb all the way to the top to see 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 down the alternate path past the Heart Tank without it; another metal block completely blocks the way just before the Light Capsule and a couple more after it. They can only be destroyed with these one of these powers. Alternatively, Zero can reach the overhang with the Jumper part and X can reach it with the Hyper Dash and Jumper parts.

Weapon Sub Tank
Function: Works identically to the health Sub Tanks, except for weapon energy instead of health.

Location: Shield Sheldon's stage

Requirements: None; Shadow Armor can be used

It sits on a bed of spikes in plain sight early on in the stage's Nightmare Zone. The Zone is accessed from the portal at the end of the main stage's 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 the portal. Once you see the Weapon Tank, get hit by the enemy just before it, 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.

EX (Life) Tank
Function: Technically not a Sub Tank in the traditional sense, once you obtain it, whenever you load a saved game or game over on a stage, you will restart that level with four lives spare instead of the standard two lives.

Location: Blizzard Wolfang's stage

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

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). Head right through here and drop down one level. If you drop down the spike lined shaft, you will observe the EX Tank lying on a bed of spikes, and a platform with a Rescuable Reploid just to the right of that. It may be best to take a death now to observe the lay of the land. The easiest way to obtain it is to simply use the Shadow Armor to walk on the spikes. However, by using the Falcon Armor or Zero's air dash, you can nab the EX and die in the process. Alternatively, you can use the Falcon Armor or Zero's air dash, or even more easily with the Blade Armor's mach dash, to reach the platform with the Reploid, and then jump back to the left obtaining the EX Tank and dying in the process. It is actually possibly to make it back without dying using this method if you use the mach dash. Even more intriguingly, odd hitboxes allow you to use the Falcon Armor or Zero's air dash, or the Blade Armor's mach dash, to obtain the EX Tank from the left in mid-air AND make it to the platform with the Reploid without dying either. Although this is quite precise, it is easier with the mach dash than a type of air dash. Using a vertical mach dash, you can also reach the area above the spike shaft and climb down the other side to approach the EX Tank from the right instead too. Ultimate Armor can likely be used in similar or the same ways to the Blade Armor to obtain it too.

Obtaining the EX Tank in X6 has to be one of the most versatile methods in the series.