Mega Man X3/Heart Tanks

Neon Tiger
At the end of the stage, before you can go through the first boss gate, backtrack until you see the last dragonfly platform, get on the top of it, wait until the platform goes near the wall, dash jump off the platform, climb up the wall to get the Heart Tank. You can also perform a vertical dash to reach the wall and climb up to the Heart Tank, or even dash jump off the lower wall just above the boss gate to the wall leading to it.

Gravity Beetle
This Heart Tank cannot be obtained before defeating Blast Hornet. Crates will block the way if Blast Hornet is not defeated.

After you defeat Blast Hornet, go to the first indoor area, climb onto the higher platforms and go left. The Heart Tank should be right there. A horizontal air dash can reach the platform with the Heart Tank from the lower platform, avoiding dealing with the pesky Head Gunners on the upper platforms, however this is not absolutely necessary, just a useful shortcut.

Blast Hornet
Get the Leg Upgrade. Before you go through the door to the Bit/Byte room, air dash vertically to climb the wall to reach to the Heart Tank. The Heart Tank can also be reached without the Leg Upgrade by jumping up out of the Ride Armor you potentially unlocked a little earlier in the stage and onto the wall. You can also reach the wall by dash jumping off the lower wall, but this is extremely difficult.

Blizzard Buffalo
Unlock Ride Armors or Tornado Fang. One method is that you get on the Ride Armor platform near the start of the stage, choose one of the Ride Armors (except Frog), go to the breakable ice blocks near the platform, and smash all the ice blocks to get to the Heart Tank. The other method is to use Tornado Fang to break the ice instead. It can be broken more efficiently with Tornado Fang if you shoot them from the ladder through the wall.

Toxic Seahorse
At the top of the first vertical climb of the stage, just before the Bit/Byte room, climb up the open ceiling to get the Heart Tank.

Tunnel Rhino
Get the Triad Thunder and Arm Upgrade. Early in the stage, go through a gap in the right wall to an area where a boulder is suspended over the spikes. Charge up the Triad Thunder, release it, wait for the boulder to crash down onto the spikes, use the boulder as a platform, and get the Heart Tank.

You absolutely must revisit Tunnel Rhino's stage to obtain this Heart Tank as it requires the Arm Upgrade, which in turn requires Tunnel Rhino's Tornado Fang.

Volt Catfish
Get the Leg Upgrade. Ride on the second elevator platform, make sure it reaches to the ceiling all the way, go right, cling on the wall, but don't hit the spikes, air dash to get the Heart Tank without touching the spikes, and air dash back to the left wall. You can also obtain the Heart Tank by dash jumping off the wall to it, and it is doable to get back without dying, however it is tricky.

Crush Crawfish
Unlock Ride Armors. Get on the Ride Armor platform directly below the very beginning of the stage, select a Ride Armor (except Frog), get to the vertical tunnel, stop right after the giant reploid destroys the three connecting bridges, jump and fall down to the right. The jump will make you reach the third destroyed connecting bridge. On the second ledge down, there is a cracked wall. Destroy it, and go through to get the Heart Tank.