Here's my idea on how Tweedle could be done. (Fantasizing is fun!)

NAME: Tweedle (duh)
LOOKS LIKE: Freeze a Tweedle event and pause a split second after it thaws to see what it looks like.
STRATEGY HE USES: Jumps around, Bubba style, and occasionally stomps the ground, sending shockwaves in both directions. The shockwaves deal two hearts of damage, and you're stunned if you're on the ground when Tweedle lands, meaning you're almost certainly gonna get hurt. When his life is halfway down, he splits himself into clones (get it? Tweedle Dee and Tweedle Dum...ah never mind). They both act like the original Tweedle, but go much faster. Take out half of the remaining power to kill one clone. Now the remaining Tweedle goes MUCH faster, and is basically a killer. At this final phase (remaining Tweedle would have a quarter of a lifebar left), demonic chesire cats rise from below the ground, and hurt you in addition to the attacks of Tweedle himself. Take out his remaining life and he's FINALLY defeated.

Here's a boss that could additionally work with Robot Devan boss, but can be used standalone too:

NAME: Power Core
LOOKS LIKE: Two large pillars from both floor and roof. Two giant cannons attached to the front and back of the bottom pillar. Between the pillars is a large diamond shaped energy.
STRATEGY IT USES: The trick is, the power core is COMPLETELY invincible to conventional attacks. The lasers the cannons shoot reflect off walls and are basically homing. Lure the lasers into the weak point of the core to damage it, and eventually defeat it. If Robot Devan is being used, text will be displayed and he will warp away.

'Nother boss!

NAME: Rock Gargoyle
LOOKS LIKE: Picture a gargoyle looking like Devil Devan second phase completely stony textured with a green gem in the forehead.
STRATEGY: It flies around slowly, shooting Bilsy style homing fireballs. Occasionally it lands and flaps its wings quickly, sending tornadoes at J/S/L. The green gem is the gargoyle's only weak point. Also, sometimes the gargoyle flies offscreen and returns, slamming the ground, and destroys one masked tile it lands on (so place warps or hurts below). Destroy the gem, and the gargoyle falls apart and dies.

Phew! That took a while to type out! Enjoy it.