On level 236 it is very easy to get power-ups at the top of the field and the bottom is covered by granite that can only be destroyed with bombs and dynamite. It is easy to make firecrackers, but their area of effect will not reach the granite, and if you wait too long for dynamite and warheads to appear you can just run out of moves.
You really need to pay attention to the location of the portals. The exits and entrances are not located one above the other, as you might expect. The right upper part of the level is connected to the lower left one and vice versa. This gives you the freedom of maneuver.
Instead of trying to get a dynamite power-up, assemble one or two bombs in the same part of the field and then position them on top of a portal. Then collect a bomb on the other side of the field, set it off so that the explosion destroys some of the granite below. The bombs you prepared on the other side will fall into the emptied space. Detonate them there and your chances of winning will increase greatly!
You should also check out this video that shows how we got through level 236.