Custom Featured block example : http://prntscr.com/k4e4z9

functions.php

add_filter('vibe_builder_thumb_styles',function($thumb_array){
    $thumb_array['custom_block']= 'https://i1.wp.com/i.imgur.com/gxrPvvJ.jpg?zoom=2&w=920';
    return $thumb_array;
});

add_filter('vibe_featured_thumbnail_style',function($thumbnail_html,$post,$style){
    if($style == 'custom_block' && $post->post_type == 'course'){ //Custom block is the same name as added for the thumbnail in pagebuilder
        $thumbnail_html ='';
        $thumbnail_html .= '<div class="block customblock">';
        $thumbnail_html .= '<div class="block_media">';
        $thumbnail_html .= '<a href="'.get_permalink($post->ID).'">'.get_the_post_thumbnail($post->ID,'medium').'</a>';
        $thumbnail_html .= '</div>';
        $thumbnail_html .= '<div class="block_content">';
        $thumbnail_html .= '<h4 class="block_title"><a href="'.get_permalink($post->ID).'" title="'.$post->post_title.'">'.$post->post_title.'</a></h4>';
        $thumbnail_html .= '<p class="block_description">'.get_the_excerpt($post->ID).'</p>';
        ob_start();
        the_course_button($post->ID);
        $thumbnail_html .= ob_get_clean();
        if(is_user_logged_in()){
        	$user_id = get_current_user_id();
        	if(bp_course_is_member($post->ID,$user_id)){
        		$progress = bp_course_get_user_progress($user_id,$post->ID);
        		if(empty($progress)){
        			$progress = 0;
        		}
        		$thumbnail_html .= do_shortcode('[progressbar percentage="'.$progress.'" bg="#eee" bar_color="42a1f4"]');
        	}else{
        		$thumbnail_html .= bp_course_get_course_credits(array('id' => $post->ID));
        	}
        }else{
        	$thumbnail_html .= bp_course_get_course_credits(array('id' => $post->ID));	
        }
        
        $thumbnail_html .= '</div>';
    }


    return $thumbnail_html;
},10,3);

add_action('wp_footer',function(){
?>
<style>
.block.customblock {
    border: 2px solid #333 !important;
    border-radius:15px;
}

.block.customblock .block_content {
    padding: 15px 30px;
    text-align: center;
}


.block.customblock .block_content a.button {
    display: inline-block;
    text-align: center;
    font-size: 16px;
    opacity: 0.6;
    background: #aaa;
}

.block.customblock .block_content strong {
    display: block;
}

.block.customblock h4.block_title {
    font-size: 20px;
    font-weight: 600;
    margin: 10px 0 15px;
}

.block.customblock .block_content a.button:before {
    content: "\f023";
    font-family: fontawesome;
    margin-right: 5px;
}
.block.customblock .block_content input.button{padding-left:30px;}
.block.customblock .block_content form:before{
    content: "\f09c";
    font-family: fontawesome;
    margin-right: 5px;
    position:absolute;
    z-index:99;
    margin:18px 10px;color:#fff
}
</style>
<?php
});