User:Prime Raptor21/hotcrystal0 reaction
In the hotcrystal0 reaction, a glider hits a block, with the resulting mess modified to replace the block. A spark is needed at generation 16, this spark can be provided with a sparker with a period as low as 3. However, a unix is smaller when it works. The block reappears at generation 31.
Using this reaction, some stuff can be made. As AbhpzTa points out, a transparent beehive and opaque eater can edgeshoot a glider from the reaction. The beehive and eater can go on the other way, however this is less useful.
As wwei23 points out, a unix can liberate an octomino from the reaction, while optionally creating an extra glider (the extra glider only works at P6). A killer toad can then turn the octomino into a glider. As a splitter, guns with period 174+24n can be created. As a reflector, the repeat time is 60.