Mega Man X3/Heart Tanks

Neon Tiger
At the end of the stage, before you can go through the first 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.

Gravity Beetle
This Heart Tank cannot be obtained before beating Blast Hornet.

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.

Blast Hornet
Get Leg Upgrade. Before you go to the door where it leads to Bit (or Byte if you have destroyed Bit), Air Dash vertically to climb the wall to reach to the Heart Tank.

Blizzard Buffalo
Get at least two Robot Walkers or Tornado Fang. One method is that you get on the Robot Walker Platform, choose one of the Robot Walkers (except Frog), go to the breakable ice blocks near the platform, and smash all the ice blocks to get to the Heart Tank. Another method is to use Tornado Fang instead.

Toxic Seahorse
At the area where the green water is falling, climb up the open ceiling to get the Heart Tank.

Tunnel Rhino
Get Triad Thunder and X-Buster Upgrade. Reach to the area where the boulder is suspended over the spikes. Charge up the Triad Thunder, wait for the boulder crashing down onto the spikes, use the boulder as a platform, and get the Heart Tank.

Volt Catfish
Get 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.

Crush Crawfish
Get at least two Robot Walkers. Get on the Robot Walker Platform, select it (except Frog), get to the vertical tunnel, reach to the cracked right wall, smash it, and go through to get the Heart Tank.